Because it may participate and enjoy the returning tide. This is done, as well as the shell closed, with prodigious force, by means of a strong muscle at the hinge.

Mr. Carew, in his Survey of Cornwall, 1602, tells us of an oyster having opened its shell, and three mice attempting to seize it; but the oyster clasped fast its shell, and killed them all.

THE MUSSEL.

Why is the common mussel enveloped in a thread-like substance termed byssus?

Because these threads are united in the body to a secreting gland, furnished with powerful muscles, and, at the other extremity, glued to the rock or other body to which it connects itself.-Fleming.

Why are the pinna, or sea-wings prized?

Because of their beard, by means of which they attach themselves, and from which gloves, &c. are manufactured at Smyrna, Tarentum, Palermo, &c. A pair of gloves made of this material may be seen in the British Museum.

PEARLS.

Why are pearls found in the oyster?

Because they consist of the morbid secretions of the fish, situated either in the body, or lying loose between, it and shell; or, lastly, fixed to the latter by a kind of neck. It is said they do not appear until the animal has reached its fourth year. There is nothing peculiar in their chemical composition, being merely carbonate of lime.

The Romans gave almost incredible prices for pearls. Their finest pearls were from the Gulf of Persia, and the Indian Ocean; though it is matter of history that Cæsar was induced to invade Britain from some exaggerated accounts he had heard of the pearls of our coasts, or rather of our rivers; but, if

these were his objects, the mercenary conqueror was disappointed, for they were found to be of bad colour and inferior size, nor have they since improved.

Why did Linnæus owe his patent of nobility to the pearl

Because he received that elevation for a discovery of causing the fresh-water mussels of Sweden to produce pearls at his pleasure. It is conjectured that he accomplished this by drilling small holes through the shells; but his method is not certainly known.

THE NAUTILUS.

Why is the Paper Nautilus also called the Argonaut? Because of its origin from Argonautes, the companions of Jason, in the celebrated ship Argo, and from the Latin naus, a ship; the shells of all the Nautili, having the appearance of a ship with a very high poop. When sailing, the animal expands two of its arms on high, and between these supports a membrane which serves as a sail, hanging the two other arms out of its shell, to serve as oars, the office of steerage being generally served by the tail.

When the sea is calm, whole fleets of these Nautili may be seen diverting themselves; but when a storm arises, or they are disturbed, they draw in their legs, take in as much water as makes them specifically heavier, than that in which they float, and then sink to the bottom. When they rise again, they void this water by numerous holes, of which their legs are full.

The cuttle-fish, from its frequently being found in the shell of the Argonauta, was long considered the fabricator of the shell; but, more recent observation has proved it to be merely the piratical occupant.

END OF PART VIII.

KNOWLEDGE FOR THE PEOPLE:

OR THE

PLAIN WHY AND BECAUSE.

PART IX.-ZOOLOGY-INSECTS.

ZOOLOGY.

INSECTS.

GENERAL ECONOMY.

Why are insects so called?

Because they have a separation in the middle of their bodies, whereby they are cut (insectus, cut or notched, Lat.) into two parts, joined by a small ligature, as in the common house-fly.

Why are the history and descriptions of insects called Entomology?

Because of the origin of that term from the two Greek words, entoma, insects; and logos, a discourse. Why is the study of insects a source of perpetual variety 2

Because the localities of insects are, to a certain extent, constantly changing. Insects, also, which are plentiful one year, frequently become scarce, or disappear altogether the next a fact, strikingly illustrated by the uncommon abundance in 1826 and 1827, of the seven-spot lady-bird in the vicinity of London, though during the two preceding summers, this insect was comparatively scarce, while the small two-spot lady-bird was plentiful.-J. Rennie.

Why did the ancient philosophers believe that maggots, flies, and other insects, were generated from putrifying substances?

Because they were found about animal bodies in a state of decomposition; and the circumstance was merely noticed without any previous or accurate observation of the means by which they were first produced.