hours more it has entirely ceased, and the air resumes its wonted serenity.

"But, what," continues he, " has become of that prodigious quantity of flies when they no longer appear in the air? They are already dead or dying for the most part; a great, and a very great part of them have fallen into the river itself from whence they arose. The fishes have no days in the year in which they can make such a sumptuous regale, or in which they can gorge themselves with such delicate food: gluttons as they are, if they could foresee it, they would regret (like some gormandizers of the human race) that their stomachs could not receive the whole of the fine food that was at their disposal, and that they must suffer a great deal more to be lost than they could possibly deThese days are then to them days of the highest regale; manna falls upon them from heaven. The fishermen have even given to these ephemera the name of manna; and it is by that name that they are known by them along the rivers of the kingdom. They say, that the manna has begun to appear, or that the manfell in abundance on such a night, in order to denote that they have begun to perceive the ephemera, or that they have appeared in great abundance.

vour.

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"Those which have fallen into the water and are not the prey of fishes, perish alike with the others; they are instantly drowned. The life of those which fall upon the banks of the river is not quite so short; but it had been better for them that their lives had been curtailed. Heaped above each other, without having sufficient force to move, they must remain in a very disstressed condition until they die."

Our author farther observes, that however short the

life of this fly is, it is sufficient to give them time to fulfil the only end for which they seem to have been produced; that of perpetuating the species: or rather, as he says, considering the short time that it remains in the fly state, to perpetuate the aquatic worms and the nymphs which proceed from them. The female ephemera appear to have no other business than to lay their eggs; and they seem to be in a condition to do this almost as soon as they are produced. The body of the female, if it be examined when even in its nymph state, is nearly filled with eggs. These eggs are disposed in the form of two large packets, each packet containing from 300 to 400 eggs; nor are these eggs deposited by the fly in succefsion, as in most other cases, but both the packets of eggs are extruded from the body at one time, through two openings formed for that purpose, and fall together in one accumulated mafs. To enable the creature to extrude these, and at the same time to fill up the great vacuum in the abdomen that must thus instantaneously take place, the fly is provided with a couple of air-bladders, which it has the power of filling with air, and thus extruding the ovaries, and occupying their place.

One other singularity respecting this insect deserves to be particularly noticed; because, like that just mentioned, it concurs in facilitating those rapid operations which the short life of this insect renders so necessary. It is the facility with which they are born, as Reaumur exprefses it, that is to say, with which they strip themselves of the slough of the nymph. The operation of casting off the exuviæ of the chrysalis, or nymph, to most insects is attended with much diffi

vouring to effect it. But to the ephemera it is far from being so. "None of the insects that I know," says Mr. Reaumur, "executes an operation so great, which seems to be so laborious, and which really is so to the greatest part of them,, with so much ease, and celerity. The tub of which I have so often spoken, enabled me to observe them better than I could have done upon the river only. We do not draw our arm more quickly from the sleeve of a coat, than the ephemera draws its body, its wings, its legs, and the long filaments of its tail, from that complicated vestment which forms a kind of sheath for all these parts. Those ephemera who were about to transform themselves, whether upon the clods of earth in the tub, or even upon the surface of the water, had no sooner effected a rent in the corcelet, and that corcelet began to appear through that rent, than the rest of the operation was finished in an instant. I have often endeavoured to retard their progrefs, in order the better to observe how each part was contained within its respective sheath; I have seized a fly which began to disengage its head; I have prefsed the head in the very instant when it began to show itself; I have even pushed the cruelty so far as to flatten and bruise the head under my fingers; but the metamorphosis, which I wished to suspend, was accomplished in spite of me. I have thrown into spirit of wine ephemera which had only escaped in part from their case; they, however, completely divested themselves of their exuviæ in that powerful liquor, and perished immediately. Sometimes, indeed, it happens, that the filaments of the tail cannot be so quickly disengaged as the rest, sq VOL. III.

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that they fly away with their slough appended, and sometimes also these slender filaments are thus broken off.

Even short, however, as its life in the fly state is, this insect has to submit to one very difficult operation while in this state, that few of the longer lived insects undergo. It even quits another complete slough, over the whole body, wings, tail, and every other member after it has assumed its pupa state. But it is not surprising, if naturalists have not had oportunities of remarking these peculiarities with perfect accuracy. Reaumur was imperfectly acquainted with this operation, and obscurely describes it in one of the species. Geoffrey describes it more particularly; but not having adverted to the insect in its aquatic nymph state, he conceives it to be first a winged nymph that flies in the air before it afsumes its pupa state. He observes, that when it is ready to change its state it rises to the surface of the water, and instantly quits its skin and becomes a winged nymph, flying to the first object it meets with, where it leaves a second slough, thin, white, and transparent, which is often found in summer attached to the panes of glafs in windows, and then beomes a perfect fly. Reaumur describes the same phenomenon respecting a small diurnal ephemera which he once fell in with as he was travelling, and which covered the glafs of the windows of his carriage with their exuviæ. It is fully explained by De Geer. The male of this kind of fly is easily distinguished from the female, and chiefly by means of the length of the fore legs and the tail. The females have always three long filaments in the tail, of which that in the

there; but that in the middle is by much the shortest, it being not one fourth part the length of the others, but the fore legs of the males extend much farther than those of the female flies. There are other characteristic differences also which it is unnecessary here to specify.

There are many varieties of this clafs of insects, (Fabricius describes sixteen sorts, all of them natives of Europe except one, which is of Morocco) which differ from each other in diverse particulars, though they agree in regard to their general mode of living, and principal changes.-The larvæ of the whole live in the water and are transformed into vivaceous nymphs, which move about, and require food, while in that state. These larvæ have all six legs, pincers in the fore part of their head, and a long and slender body, with filamentous tails; but these filaments differ in conformation, and arrangement of their parts. They are all endowed with that set of organs which some have denominated gills, but these also differ greatly in their conformation, as has been already said. The larvæ vary also in regard to their mode of living, most of them moving about in the bottom of the water among the mud, without attempting to make holes in the banks. There are, however, considerable diversities in respect to the duration of their lives, both in their larvæ and pupa state; some of them continuing at least, three years in the form of an aquatic insect; and some of them have been known to exist in their pupa state for several weeks. De Geer mentions one kind that has only one pair of wings. But it is unnecessary for us to enter farther into the particulars of these details on the present occasion.