From the earliest time, pearls have been considered as valuable ornaments; they are mentioned in the book of Job, (see chap. xxviii, verse 18th.,) and are often alluded to by Greek and Roman writers. Various attempts have been made to imitate them, and one mode of producing them, practised, it is said, more than a thousand years ago, is still carried on in China. In the shells of Pearl Oysters, holes are bored, into which pieces of iron are introduced; these wounding and irritating the animal, cause it to deposit coat upon coat of pearly matter over the wounded part, and so the pearl is formed. Artificial pearls are made of hollow glass globules or little globes, covered on the inside with a liquid called pearl-essence, and filled up with white wax. Historians speak of an ancient traffic in native pearls carried on by this country; and in modern times, British pearls of considerable value have been discovered, one not many years since, by a gentleman who was eating oysters at Winchester, was valued at two hundred guineas. Generally, however, the pearls of this country are inferior in the two requisites of colour and size. Interesting accounts of Pearls and Pearl-fishing, will be found in “the Penny,” and “Saturday Magazines,” and many other works easy of access. There our young readers may learn of the perils and dangers to which the poor divers are exposed from the voracious sharks, which hover about the fishing grounds, and make a dash at their victim, heedless of the written charms, with which the priest or shark-charmer has provided him previous to his descent, and of much more than we can find space here to tell. All we can now do is to give the portrait, as drawn by Thomas Hood, of a lady who takes up her abode in all the pearl-producing bivalves, and who is therefore, perhaps on this account, called [Illustration: THE MOTHER OF PEARL.] THE MUSSEL AND THE COCKLE. It is in the _Dimyaria_ division of the _Conchifera_ that we must look for these familiar bivalves, the Mussel, or, as it is sometimes spelled, Muscle, and the Cockle; the former called in scientific language _Mytilus_, which in Latin means simply a shell-fish, and the latter _Cardium_, which may have reference to the hinge of this bivalve, or the heart-shape assumed by several of the species; _cardo_, in Latin, signifying the hinge of a gate, and _cardesco_, a stone in the shape of a heart.