Chamberss Edinburgh Journal, No. 437 | Page 9

the districts
watered by the Seine and the Marne in such abundance, that the
fishermen of these rivers believe it is showered down from heaven, and
accordingly call its living clouds, manna. Reaumur once saw the
May-flies descend in this region like thick snow-flakes, and so fast, that
the step on which he stood by the river's bank was covered by a layer

four inches thick in a few minutes. The insect itself is very beautiful: it
has four delicate, yellowish, lace-like wings, freckled with brown spots,
and three singular hair-like projections hanging out beyond its tail. It
never touches food during its mature life, but leads a short and joyous
existence. It dances over the surface of the water for three or four hours,
dropping its eggs as it flits, and then disappears for ever. Myriads come
forth about the hour of eight in the evening; but by ten or eleven o'clock
not a single straggler can be found alive.
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.
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 insect, in fact,
circulates air instead of blood. As the prick of the finest needle draws
blood from the flesh of the backboned creature, it draws air from the
flesh of the insect. Who will longer wonder, then, that the insect is so
light? It is aerial in its inner nature. Its arterial system is filled with the
ethereal atmosphere, as the more stolid creature's is with heavy blood.
If the reader has ever closely watched a large fly or bee, he will have
noticed that it has none of the respiratory movements that are so
familiar to him in the bodies of quadrupeds and birds. There is none of
that heaving of the chest, and out-and-in movement of the sides, which
constitute the visible phenomena of breathing. In the insect's economy,
no air enters by the usual inlet of the mouth. It all