Part 14 (2/2)

The gnat, or musquito, culex pipiens. The larva of this insect lives chiefly in water, and the pupa moves with great agility. It is fished for by ducks; and, when it becomes a fly, is the food of the young of partridges, quails, sparrows, swallows, and other small birds. The females wound us, and leave a red point; and in India their bite is more venomous. The male has its antennae and feelers feathered, and seldom bites or sucks blood; Lin. Syst. Nat.

It may be driven away by smoke, especially by that from inula helenium, elecampane; and by that of cannabis, hemp. Kalm. It is said that a light in a chamber will prevent their attack on sleeping persons.

The gnats of this country are produced in greater numbers in some years than others, and are then seen in swarms for many evenings near the lakes or rivers whence they arise; and, I suppose, emigrate to upland situations, where fewer of them are produced. About thirty years ago such a swarm was observed by Mr. Whitehurst for a day or two about the lofty tower of Derby church, as to give a suspicion of the fabric being on fire.

Many other kinds of flies have their origin in the water, as perhaps the whole cla.s.s of neuroptera. Thus the libellula, dragon fly: the larva of which hurries amid the water, and is the cruel crocodile of aquatic insects. After they become flies, they prey princ.i.p.ally on the cla.s.s of insects termed lepidoptera, and diptera of Linneus. The ephemera is another of this order, which rises from the lakes in such quant.i.ties in some countries, that the rustics have carried cart-loads of them to manure their corn lands; the larva swims in the water: in its fly-state the pleasures of life are of short duration, as its marriage, production of its progeny, and funeral, are often celebrated in one day. The phryganea is another fly of this order; the larva lies concealed under the water in moveable cylindrical tubes of their own making. In the fly-state they inst.i.tute evening dances in the air in swarms, and are fished for by the swallows.

Many other flies, who do not leave their eggs in water, contrive to lay them in moist places, as the oestros bovis; the larvae of which exist in the bodies of cattle, where they are nourished during the winter, and are occasionally extracted by a bird of the crow-kind called buphaga. These larvae are also found in the stomachs of horses, whom they sometimes destroy; another species of them adhere to the a.n.u.s of horses, and creep into the lowest bowel, and are called botts; and another species enters the frontal sinus of sheep, occasioning a vertigo called the turn. The musca pendula lives in stagnant water; the larva is suspended by a thread-form respiratory tube; of the musca chamaeleon, the larva lives in fountains, and the fly occasionally walks upon the water. The musca vomitoria is produced in carcases; three of these flies consume the dead body of a horse as soon as a lion. Lin. Syst. Nat.

ADDITIONAL NOTE. V.

AMPHIBIOUS ANIMALS.

So still the Diodons, amphibious tribe, With twofold lungs the sea and air imbibe.

CANT. I. l. 331.

D. D. Garden dissected the amphibious creature called diodon by Linneus, and was amazed to find that it possessed both external gills and internal lungs, which he described and prepared and sent to Linneus; who thence put this animal into the order nantes of his cla.s.s amphibia. He adds also, in his account of polymorpha before the cla.s.s amphibia, that some of this cla.s.s breathe by lungs only, and others by both lungs and gills.

Some amphibious quadrupeds, as the beaver, water rat, and otter, are said to have the foramen ovale of the heart open, which communicates from one cavity of it to the other; and that, during their continuance under water, the blood can thus for a time circulate without pa.s.sing through the lungs; but as it cannot by these means acquire oxygen either from the air or water, these creatures find it frequently necessary to rise to the surface to respire. As this foramen ovale is always open in the foetus of quadrupeds, till after its birth that it begins to respire, it has been proposed by some to keep young puppies three or four times a day for a minute or two under warm water to prevent this communication from one cavity of the heart to the other from growing up; whence it has been thought such dogs might become amphibious. It is also believed that this circ.u.mstance has existed in some divers for pearl; whose children are said to have been thus kept under water in their early infancy to enable them afterwards to succeed in their employment.

But the most frequent distinction of the amphibious animals, that live much in the water, is, that their heart consists but of one cell; and as they are pale creatures with but little blood, and that colder and darker coloured, as frogs and lizards, they require less oxygen than the warmer animals with a greater quant.i.ty and more scarlet blood; and thence, though they have only lungs, they can stay long under water without great inconvenience; but are all of them, like frogs, and crocodiles, and whales, necessitated frequently to rise above the surface for air.

In this circ.u.mstance of their possessing a one-celled heart, and colder and darker blood, they approach to the state of fish; which thus appear not to acquire so much oxygen by their gills from the water as terrestrial animals do by their lungs from the atmosphere; whence it may be concluded that the gills of fish do not decompose the water which pa.s.ses through them, and which contains so much more oxygen than the air, but that they only procure a small quant.i.ty of oxygen from the air which is diffused in the water; which also is further confirmed by an experiment with the air-pump, as fish soon die when put in a gla.s.s of water into the exhausted receiver, which they would not do if their gills had power to decompose the water and obtain the oxygen from it.

The lamprey, petromyzon, is put by Linneus amongst the nantes, which are defined to possess both gills and lungs. It has seven spiracula, or breathing holes, on each side of the neck, and by its more perfect lungs approaches to the serpent kind; Syst. Nat. The means by which it adheres to stones, even in rapid streams, is probably owing to a partial vacuum made by its respiring organs like sucking, and may be compared to the ingenious method by which boys are seen to lift large stones in the street, by applying to them a piece of strong moist leather with a string through the centre of it; which, when it is forcibly drawn upwards, produces a partial vacuum under it, and thus the stone is supported by the pressure of the atmosphere.

The leech, hirudo, and the remora, echeneis, adhere strongly to objects probably by a similar method. I once saw ten or twelve leeches adhere to each foot of an old horse a little above his hoofs, who was grazing in a mora.s.s, and which did not lose their hold when he moved about. The bare-legged travellers in Ceylon are said to be much infested by leeches; and the sea-leech, hirudo muricata, is said to adhere to fish, and the remora is said to adhere to s.h.i.+ps in such numbers as to r.e.t.a.r.d their progress.

The respiratory organ of the whale, I suppose, is pulmonary in part, as he is obliged to come frequently to the surface, whence he can be pursued after he is struck with the harpoon; and may nevertheless be in part like the gills of other fish, as he seems to draw in water when he is below the surface, and emits it again when he rises above it.

ADDITIONAL NOTE. VI.

HIEROGLYPHIC CHARACTERS.

So erst as Egypt's rude designs explain.

CANTO I. l. 351.

The outlines of animal bodies, which gave names to the constellations, as well as the characters used in chemistry for the metals, and in astronomy for the planets, were originally hieroglyphic figures, used by the magi of Egypt before the invention of letters, to record their discoveries in those sciences.

Other hieroglyphic figures seem to have been designed to perpetuate the events of history, the discoveries in other arts, and the opinions of those ancient philosophers on other subjects. Thus their figures of Venus for beauty, Minerva for wisdom, Mars and Bellona for war, Hercules for strength, and many others, became afterwards the deities of Greece and Rome; and together with the figures of Time, Death, and Fame, const.i.tute the language of the painters to this day.

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