FOURTH WEEK-SATURDAY.

REPRODUCTION OF INSECTS.-THEIR EGGS.

I HAVE already taken some notice of the eggs of insects, in reference to the qualities with which they are endowed for resisting the rigours of winter.* It may now be proper to say a few words regarding their general properties and peculiarities, as well as the instincts belonging to the female, which secure their deposition in the most proper situations.

It has been remarked by some naturalists, that the eggs of insects, which are of very various shapes and colours, have, at least in many instances, expansible shells, which enables them to increase in size, according to the progressive development of the enclosed larva. The younger Huber discovered this quality in the eggs of ants, and others have observed the same gradual enlargement, along with change of shape, in those of other insects. The design of the Creator in this expansible property, is sufficiently. obvious, and there are some natural contrivances in certain eggs, the final cause of which we can also distinctly trace. The eggs of the ephemeræ, for example, are smooth and oblong, resembling carraway comfits, a form, which Swammerdam mentions, as admirably adapted for diffusing them through the water, where he says they are dropt by the mother insect. To prove this, he placed a few of them on the point of a knife, and letting them fall gently into the water, they immediately separated of themselves, in a very curious manner." The same accurate observer describes a very remarkable appendage in the egg of the water scorpion. This egg is furnished with a coronet of seven bristles, disposed like down on the seed of the blessed-thistle. These bristles closely embrace the egg next to them in

"Winter," p. 139, &c. † Book of Nature, vol. i. p. 204.

the ovary of the mother insect. As these eggs are deposited in the stems of aquatic plants, the bristles, which are partly left on the outside, are probably intended to prevent the aperture from being closed by the rapid growth of the plant. Reaumur gives an interesting description of similar eggs, deposited by a common dung fly. These eggs are furnished at the upper end with two diverging pegs, which prevent them from sinking into the dung, where they are placed by the parent, while they are permitted to enter sufficiently far to preserve them moist. Both circumstances are indispensable to their hatching; for when Reaumur took them out of the dung, they shrivelled up in a few hours, and when he immersed them farther than the pegs, they were suffocated, and could not afterward be hatched.*

A still more remarkable appendage belonging to some insects' eggs, is that of a foot-stalk, evidently intended to place them out of the reach of grubs, which might devour them. The eggs of the lace-winged fly is of this description. They consist of a small oval greenish-white head, similar to apple mould, with a white transparent stem, more than an inch high, and not thicker than a human hair, but smaller, and more stiff and rigid. About a dozen of these eggs are deposited by the fly in a single, and sometimes in a double, line, upon the leaves or branches of the elder, and of other trees and plants, abounding with aphides, upon which the grubs feed when hatched. The foot-stalks of these eggs are formed by the mother fly attaching a drop of gluten to the branch, and drawing it out to the requisite length, before the egg is deposited on its summit. As she uses her body for a measure, the foot-stalks are all of one length. They are so smooth and slender, that the grubs could not climb upon them.

Many eggs are immersed in a glutinous liquor, by which they are made to adhere to trees, or other substances on which they are deposited, or united together

* Reaumur, Mem. iv. p. 37.

in various forms, and for various purposes of safety. In the "Winter" volume, I noticed the remarkable instance of the gipsy moth, which, by means of this gluten, not only fixes her eggs to the tree and to each other, but covers them over with down taken from her own body, to preserve them from the inclemency of the weather. A still more admirable use of this glutinous fluid is made use of by the common gnat, which is too curious to be passed over. It is described by Reaumur, who, by repairing to a pond, or bucket of standing water, before five, or at latest, six in the morning, frequently witnessed the remarkable operation ; and it has also been seen and described by other naturalists.

The problem of the gnat is to construct a boat-shaped raft which shall float, of eggs heavy enough to sink in water, if dropped into it one by one. The eggs are nearly of the pyramidal form of a pocket gunpowder-flask, rather pointed at the upper, and broad at the under end, with a projection like the mouth of a bottle. The first operation of the mother-gnat is to fix herself by the forelegs (four in number) to the edge of the pond, or on a floating leaf, with her body level with, and resting upon, the surface of the water, excepting the last ring of the tail, which is a little raised. She then crosses her two hind legs in the form of an X, the inner opening of which is intended to form the scaffolding of her structure. She accordingly brings the inner angle of her crossed legs close to the raised part of her body, and places in it an egg covered with gluten. On each side of this egg she places another, all which adhere firmly together by means of their glue, and form a triangular figure, which is the stern of the raft. She proceeds in the same manner to add egg after egg, in a vertical (not horizontal) position, carefully regulating the shape by her crossed legs. As her boat increases in magnitude, she pushes the whole gradually to a greater distance, and, when she has about half finished, she uncrosses her legs and places them parallel, the angle being no longer neces

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sary for giving the proper shape. Each raft consists of from 250 to 350 eggs, which, when all laid, float on the water secure from sinking, and are finally abandoned by the mother. They are hatched in a few days, the grubs issuing from the lower end ; but the boat, now composed of the empty shells, continues to float till it is destroyed by the weather.* Kirby justly describes this little vessel as resembling a London wherry, being sharp and high, as sailors say, fore and aft, convex below and concave above, and always floating on its keel. "The most violent agitation of the water,” he adds, “cannot sink it, and, what is more extraordinary, and a property still a desideratum in our life-boats, though hollow, it never becomes filled with water, even when exposed."

The sequel of this extraordinary mode of reproduction is not less curious. The larvæ, when hatched, drop to the bottom of the water, and are there transformed into pupa. About eight or ten days after this transformation, the pupa prepares, generally about noon, for emerging into the air, raising itself up to the surface, so as to elevate its shoulders just above the level of the water. It has scarcely got into this position for an instant, when, by swelling the part of its body above the water, the skin cracks between the two breathing tubes, and immediately the head of the gnat makes its appearance through the rent. The shoulders instantly follow, enlarging the breach. The most important, and indeed indispensable, part of the process, is the maintaining of its upright position, so as not to get wetted, which would spoil its wings, and prevent it from flying. Its chief support is the envelope which it is throwing off, and which now serves it as a life-boat, till it get its limbs set at liberty and trimmed for flight. The body of the insect serves this little boat for a mast. When it has extricated itself all but the tail, it first stretches out its two fore-legs, and then the middle pair, bending them down to feel for the water, upon which it is able to walk as upon dry

* Reaumur, Mem., iv. p. 621.

land, the only aquatic faculty which it retains after having winged its way above the element where it spent the first stages of its existence.*

This is but one instance, though a very striking one, selected out of cases almost innumerable, in which astonishing and unexpected means are made use of for the preservation of animals, and especially of insects, in their earliest state. In contemplating such cases, imagination seems scarcely to keep pace with the reality. Here is a creature, committed, in its embryo form, to the surface of the water, in a life-boat constructed and launched by a parent to whom submersion is death; sinking, when developed, to the bottom of these waters, to which its life is fitted, where alone, indeed, it can live, and where it passes from one stage of existence to another; then, at the appointed time, rearing its head above its watery habitation,—becoming all at once an inhabitant of another element, spurning both the water and the land, and floating aloft on transparent wings in the balmy air. The transformation of insects, itself a miracle, is familiar to us; but the circumstances attending the changes of this little gnat, seem to have been contrived for the express purpose of exhibiting, in peculiarly interesting and remarkable combinations, the various properties of Creative skill, contrivance, adaptation, and forethought. So that, were there no other proof of these attributes in the universe, it would be impossible to mistake them here, or to withhold from the Creator the tribute of admiration.

* Insect Transformations, pp. 317, 318.