Hunter, who counted more than a thousand in one organ of five or six-sided prisms (B), with their bases presented to one surface of the fish, and their apices to the other. These are divided horizontally by numerous septa; the interspaces being filled up with a gelatinous fluid. An immense quantity of nerves pervade these prisms, on the integrity of which the power of communicating the shock depends; for their division is fatal to it. The electricity of the back is positive, and of the under surface negative; and in order to feel the shock a circuit must be made between them. Sir Humphrey Davy succeeded in his experiments on this curious fish, even to heating platina wire, decomposing acidulated water and iodide of potassium, besides actually magnetising needles in a helix. The electric organs of the Gymnotus, already mentioned, are essentially the same, in structure as those of the Torpedo, though differing in shape, in accordance with the conformation of the animal. They occupy one-third of its whole bulk, and run along nearly its entire length; there are, however, two distinct pairs, one much larger than the other. The prisms are here less numerous, but are much longer, for they run in the direction of the length of the body, a difference which is productive of a considerable modification of the character of the discharge. Even slices of an electric organ, entirely separated from the body, except by a nervous fibre, may exhibit electrical properties. Discharges may be excited by irritation of the brain when the nerves are entire, or of the part of the divided trunk distributed on the organ; but on destroying the electric lobe of the brain, the electric power of the brain ceases entirely. It is remarkable, however, that after the section of the electric nerves, torpedoes appear more lively than before the operation, and actually live longer than others which are excited to discharge frequently. The uses of these electric organs it is somewhat difficult to explain. A friend of the writer's saw a small fish, provided for the food of a gymnotus, receive a shock, on passing under the body, which killed it instantly, after which it was devoured by the eel. But these creatures, like the torpedoes, eat very few of the fishes which they kill. Dr. Carpenter suggests that this peculiar action may assist the digestion of the fish, as animals killed by electricity are more digestible. The electrical condition of the animal itself, he also thinks, may conduce to the easy digestion of its food. THE MYXINE.* THIS fish Linnæus regarded as belonging to the class Vermes; while Modeer placed it among the Amphibia. It is, however, one of the lowest in structural organisation among the fishes. It is shaped like an eel, and measures, when full grown, about one foot and a half. The Myxine is a deadly foe to fish, into the bodies of which it enters, and eats up all the fleshy parts, leaving all the skin and bones. Nillson says that several have been found in the body of a single haddock, which was all eaten away internally. The cod-fishers of Scarborough and Berwick often capture this fish in the bodies of cod or haddock drawn up by their lines, and some believe it enters their mouths while they are held and drawn up by the hook. But Cuvier says it attacks and pierces the fish: aided, perhaps, by the sense of touch implanted in its feelers, it may have the power of suddenly fixing itself by means of its hooked palatal teeth, and then, boring and rasping with its lingual teeth, insinuates itself beneath the skin, and gradually works its way into the very body of the victim. On some parts of our eastern coast it is therefore called "the borer." This fish is of a dark bluish-brown colour above, and whitish beneath. It is not uncommon in the Scandinavian seas, and is frequently taken upon the north-east coast of Britain. It does not stand alone, but is one of a genus of cartilaginous fishes, of the order Cyclostomi. We are unable to give more space to the consideration of Fish, of which several thousand specimens may be seen in the museums of Europe, every one of which has been adapted in form by the Creator to the gravity of its watery abode-whether the river or the lake, the marsh or the sea. If all fishes had been of one weight, one effort of contrivance would have enabled them all to swim; but every species of fish, almost every individual of each species, differs in its weight and size from every other. Gastrobranchus cæcus. Myxine glutinosa. EXPRESSLY designed for progression through the air, Insects compose the most extensive class of the whole Animal Kingdom. On them has been lavished, the choicest gifts of physical powers, so far as they are compatible with structures so minute. The model on which they are formed, so to speak, is that which combines the greatest security against injurious impressions from without, with the most extensive powers of locomotion, and which also admits of the fullest exercise of all those faculties of active enjoyment which characterise animal life. Thus, this part of animated Nature, like every other, eminently calculated to direct the mind to the Great Creator. "If," says the ancient writer Basil, You speak of a fly, a gnat, or a bee, your conversation will be a sort of demonstration of His power whose hand formed them; for the wisdom of the workman is commonly perceived in that which is of little size. He who has stretched out the heavens, and dug up the bottom of the sea, is also He who has pierced a passage through the sting of the bee for the ejection of its poison." Nowhere, indeed, are we so called, as in the contemplation of insects "To trace in Nature's most minute design His mighty work who speaks, and it is done!" True insects may be generally defined :-Articulated animals possessing six legs, two antennæ, two compound eyes, a small brain at the anterior extremity of a double medullary chord; circulation effected by a pulsating dorsal vessel, provided with numerous valves; respiration by trachea, which form two lateral trunks, and ramify through the body; and two distinct sexes. The final accomplishment of objects so numerous, so widely different, and so liable to mutual VOL. IV. 21 interference, is attained by each insect being subjected to a series of modifications, and passing through several intermediate stages of development. The power of flight, for instance, is never conferred on an insect in the earlier periods of its existence; but its structure obtains the lightness which fits it for rising in the air, and it acquires the instruments capable of acting on it, by going through several preparatory changes, some of which are so considerable as to justify the term of metamorphoses, which has generally been given them. So peculiar, however, are the circumstances of the egg state, the caterpillar state, the pupa state, and the imago, or perfect state, of insects, that we shall consider them separately. THE METAMORPHOSES OF INSECTS. Ir has been noticed as a singular fact that the female sheep, weeks before yeaning, selects some sheltered spot where she may drop her lamb with the most comfort and security; but the provision made by insects for their future young is far more remarkable. Other creatures attend to their progeny in the early stages of their being, but these, with few exceptions, do not live to see their EGGS OF MOTHS.-Abraxas Grossulariata. Saturnia carpini. Smerinthus populi. Pencallia syngaria. descendants. There are insects which extrude many eggs at a time, sometimes with great rapidity; while in the case of those which usually deposit their eggs singly, an interval of some minutes, hours, or perhaps even days, intervenes between the extrusion of each egg. A common moth, vulgarly called the ghost, is a singular instance of the former mode. She lays a large number of minute black eggs, resembling grains of gunpowder, and ejects them so fast that they may be said to run from the oviduct, and are sometimes expelled with the force of a pop-gun. Another insect is said to discharge her eggs like shot from a gun. And a gentleman who had observed with attention the proceedings of a common crane-fly, assured Mr. Kirby that several which he caught projected their eggs to a distance of more than ten inches. In every instance, doubtless, the mode of extrusion accords with the structure and instincts of the parent insect, while, as certainly, the egg is deposited where the caterpillar, on emerging from it, may be provided with suitable food. We have engraved some specimens of insects' eggs of the natural size and also considerably magnified. THE METAMORPHOSES OF INSECTS. 163 As the eggs of lackey moths, which are laid in the autumn are not to be hatched until the spring, the insect does not, like most other moths, place them upon a leaf, with which they might be blown far from their destined food, but upon the twig of some tree, round which she ranges them in numerous circles. With such admirable art is this done, that observing them on your fruit-trees, you would take them rather for pearls, set by the skilful hand of a jeweller, than for the eggs of an insect. Each of these bracelets, as they have been aptly termed, is composed of from two hundred to three hundred pyramidal eggs, with flattened tops, surrounding the twig in a series of from fifteen to seventeen close spiral circles, and having their interstices filled up with a tenacious brown gum, which, while it secures them alike from the wintry blast and the attack of voracious insects, serves as a foil to the white enamel of the eggs which it encompasses. How such an arrangement can be completed by insects, with their tails and feet, it is not easy to conceive. In the hope of ascertaining this, Reaumur made several experiments; but the insects, so far from disclosing the secret of their art, laid their eggs at random, and made no attempt to place them symmetrically. The egg of the gnat is shaped like an olive, or a powder-flask, and by itself would sink in water; and yet this insect glues from two hundred and fifty to three hundred in an oblong mass, which is pointed and more elevated at each end, so as to resemble in shape a little boat, which will actually swim safe and unhurt until the grubs are hatched. The lower part, on which it always floats, is convex, and the upper is concave; and so buoyant is it, that no agitation of the water, however violent, can sink it. Mr. Kirby says: "To put this to the test, I put half a dozen of these boats upon the surface of a tumbler, half full of water. I then poured upon them a stream of that element, from the mouth of a quart bottle, held a foot above them. Yet, after this treatment, which was so rough as actually to project one of them out of the glass, I found them floating as before on their bottoms, and not a drop of water within their cavity." The process by which the boat is made is very remarkable. A gnat has six legs; the four forelegs she rests on a floating leaf, or on the side of a bucket, if she is in water contained in such a vessel; and her body is thus held level with the water, except the last ring of her tail, which is a little raised. She then begins to use her two hind legs, which she crosses in the shape of the letter X, the open part of which, next the tail, serves as a kind of scaffold for the eggs she lays, until the boat is nearly formed. Each egg, when laid, is covered with a sort of glue; the gnat holds the first-laid egg in the crossed legs until the second is placed by its side, and fastened to it; she then glues to these nother egg, making a triangle; and this is the beginning of the oat. Thus she goes on, piling egg on egg, always keeping the oaf in proper shape by her useful hind legs; and as it grows a size, she pushes it from her by degrees, still adding to the nfinished end next her body. When it is of the required size and state, she flies away, and leaves to its fate, floating on the water. PINCERS AND TAIL OF GOLD-TAILED MOTH. Some moths employ a very singular covering for their eggs-hair stripped from their own bodies. |