Page images
PDF
EPUB

the folly of those desperate ineasures to which you were prompted by revenge; the advices which kept you from forming friendships which would have been a snare to you, and the warnings which taught you to detect the treachery that was concealed by smiles, and the plans of ruin which were recommended by the most plausinle assurances of gain or enjoyment. And how sad is the thought, that the spirit endowed with so much wisdom and prudence has left you to walk in your own counsels, and that painful anxieties and mistakes are before you.

PICTURES OF LIFE. In youth we seem to be climbing a hill on whose top eternal sunshine appears to rest. How eagerly we pent to attain its summit, but when we have gained it, how different is the prospect on the other side. We sigh as we contemplate the dreary waste before us, and look back with a wishful eye upon the flowery path we have passed but may never more retrace. It is like a portentous cloud, fraught with thunder, storm, and rain; but religion, like those streaming rays of sunshine, will clothe it with light as with a garment, and fringe its shadowy skirts with gold.

DEPARTMENT OF NATURAL HISTORY.

THE DRAGON-FLY A most destructive enemy of living insects is the tribe of libellula or dragon-fly, a name which they well merit from their voracious habits. The French have chosen to call them "demoiselles," from the slim elegance and graceful ease of their figure and movements. But, although their brilliant coloring, the beauty of their transparent and wide-spread wings, may give them some claim to this denomination, yet they scarcely would have received it had their murderous instincts been observed. So far from seeking an innocent nurture in the juice of fruits or flowers, they are (says Reaumur) warriors more ferocious than the Amazons. in the air only to pounce upon other insects, which they crush with their formidable fangs; and if they quit the

They hover

banks of the rivulet, where they may be seen in numbers during an evening walk, it is only to pursue and seize the butterfly or moth, which seeks the shelter. of the hedge.

The waters are their birth-place; their eggs are protruded into this element at once, in a mass which resembles a cluster of grapes.

The larva which comes out of these eggs is six-footed. The only difference between the larva and nymph is, that the latter has the rudiments of wings packed up in small cases on each side of the insect.

[graphic]

In this latter state it is supposed that the creature lives at the bottom of the water for a year. It is equally voracious then as in its perfect state. Its body is covered by bits of leaf, wood, and other foreign matters, so as to afford it a complete disguise, while its visage is concealed by a prominent mask, which hides the tremendous apparatus of serrated teeth, and serves as a pincer to hold the prey while it is devoured.

Its mode of locomotion is equally curious; for though it can move in any direction, it is not by means of feet or any direct apparatus that it moves, but by a curious mechanism, which has been well illustrated by Reaumur and Cuvier. If one of these nymphs be narrowly observed in water, little pieces of wood and other floating matters will be seen to be drawn towards the posterior extremity of the insect, and then repelled; at the same time that portion of its body will be observed alternately to open and shut. If one of them be placed

in water which has been rendered turbid by milk, or coloured with indigo, and then suddenly removed into a more limpid fluid, a jet of the coloured water will be seen to issue from the anal extremity of the libellula, to the extent sometimes of several inches; at the same time the force with which the column is ejected propels the insect in the opposite direction, by virtue of the resistance with which it meets. Hence it appears that it is by means of its respiratory system that the creature walks—a strange and anomalous combination of functions in one organ.

If the insect be taken out of the water, held with its head downwards, and a few drops of that fuid poured on its tail, that which was a mere point will immediately open and display a cavity; at the same time the

body of the insect, which was before flat, will be observed to be enlarged and inflated, and if held up to the light, semi-transparent: moreover, something solid will appear to be displaced by the water, and driven towards the head. This solid mass will shortly descend, obscure the transparency of the lower portion of the body of the insect, lessen its diameter, and, when it does so, a jet of water will issue from the vent. It is clear, then, that the abdomen of the libellula is a syringe, the piston of which being drawn up, of course the pressure of the fluid fills up the vacuum, and, when pushed down, expels the water. To ascertain the fact, Reaumur held ihe insect in his hand, and when he saw its body infla. ted, cut it immediately with a pair of scissors, and found it unoccupied with solids. He watched when the jet of water was expelled in another, and as soon as the body was darkened and lessened in diameter, he clipped it, and found the cut portion occupied by solids. There is no doubt, then, that the abdomen contains a

moveable piston, and this piston is composed of the air tubes. There are four of these longitudiral trunks,

although two only are represented, they terminate in innumerable smaller ones, and, according to Reaumur perform the functions of respiration, as well as locomotion, in the ways detailed.

After the voracious creature has lain in ambuscade, devouring the larvæ of the gnat and other aquatic insects, till its appointed hour of change, it leaves its natal element for the shore, to undergo its last metamor. phosis: for this purpose it usually fastens itself to some friendly plant, and begins the important process which is to convert an aquatic animal into an inhabitant of the air.

Any person who should at this period choose to seize a number of them, and, taking them into his chamber, fix them to a bit of tapestry, would be rewarded for his trouble by witnessing the conversion of an aquatic into an aerial insect.

It may easily be seen by the eyes of the nymph whether it is about to change its form; for, instead of remaining tarnished and opaque, they suddenly become, transparent and brilliant. This change is owing to the visual organ of the perfect insect, which is amazingly lustrous shining through the mask of the nymph. If the eye of the nymph be removed, that of the perfect insect may be seen beneath. As soon as the nymph has

fixed itself to any object by means of its claws, the first sign of the commencing metamorphosis is a rent in the upper skin, extending along the corslet to the head. When it approaches this latter part, another rent, perpendicular to the first, runs across the face from eye to eye. These rents are brought about by a power which the insect possesses of inflating its body and head. This last organ, ultimately destined to become fixed and solid, is at this period capable of contraction and dilatation, like a membrane.

The head and corslet being exposed, the legs are drawn out from their nymphine cases. At this period every part of the insect is soft. The four figures below illustrate its mode of exit.

[graphic][graphic][graphic][subsumed]

In the first (fig. 1) it is partially out; in the second (fig. 2) after having protruded itself thus far, it hangs with its head downwards, and remains motionless, 80

« EelmineJätka »