Even a particle of earth, clay, or mud may form the nucleus of a pearl. This was illustrated a few years ago in a fine button-shaped pearl, which was accidentally broken under normal usage and was found to consist of a hard lump of white clay surrounded by a relatively thin coating of nacre. More remarkable yet are the cases in which a minute fish, a crayfish, or the frustule of a diatom has formed the nucleus. Several instances have been described by Woodward, Gunther, Putnam, Stearns, and others, where small fish have penetrated between the mantle and the shell of the mollusk, and the latter has resented the intrusion by covering the intruder with a pearly coating. In two or three instances the secretion occurred in so short a time that the fish suffered no appreciable decomposition, and its species is readily identified by observation through the nacreous layer. Among the remarkable specimens of this nature which have come under our observation are two very curious shells received in March, 1907, from the Mexican fisheries. One of these specimens shows an encysted fish, so quickly covered and so perfectly preserved that even the scales and small bones are in evidence; indeed, one can almost detect the gloss on the scales of the fish; and in the other—with a remarkable comet-like appearance—a piece of ribbed seaweed is apparently the object covered. From the foregoing, it appears that the pearl is not a product of health associated with undisturbed conditions, but results from a derangement in the normal state of the mollusk. Unable to resist, to rid itself of the opposing evil, it exercises the powers given to it by a beneficent Creator and converts the pain into perfection, the grief into glory. Nature has many instances of the humble and lowly raised to high degree, but none more strikingly beautiful than this. One of the lowest of earth’s creatures, suffering a misfortune, furnishes a wonderful lesson upon the uses of pain and adversity by converting its affliction into a precious gem symbolical of all that is pure and beautiful. As written by a forgotten poet: “Forasmuch as the pearl is a product of life, which from an inward trouble and from a fault produces purity and perfection, it is preferred; for in nothing does God so much delight as in tenderness and lustre born of trouble and repentance.” As the great Persian poet Hafiz says: Learn from yon orient shell to love thy foe, And store with pearls the wound that brings thee woe. IV STRUCTURE AND FORMS IV STRUCTURE AND FORMS OF PEARLS