“This maskellez perle that boght is dere, The joueler gef fore alle hys gold, Is lyke the reme of hevenes clere”; So sayde the fader of folde and flode, “For hit is wermlez, clene and clere, And endelez rounde and blythe of mode, And commune to all that ryghtwys were.” FOURTEENTH-CENTURY MSS. OF “PEARL,” IN THE BRITISH MUSEUM. As Kadir Munshi says, “pearls have no pedigree”; their beauty is not to be traced to their origin, but exists wholly in the excellence of the surroundings in which they develop. The pearl-bearing mollusks are luxurious creatures, and for the purpose of protecting their delicate bodies they cover the interior of their shells with a smooth lustrous material, dyed with rainbow hues, and possessing a beautiful but subdued opalescence. No matter how foul, how coral covered, or overgrown with sponges or seaweeds the exterior may be, all is clean and beautiful within. This material is nacre or mother-of-pearl. It consists ordinarily of an accumulation of extremely thin semi-transparent films or laminæ of a granular organic substance called conchiolin, with the interstices filled with calcareous matter. The nacre decreases in thickness from the hinge toward the lip of the shell, and terminates a short distance from the extreme edge. Next to the nacre is the middle layer or the shell proper. In species of _Margaritifera_, this stratum is commonly formed of layers of calcareous prisms arranged vertically to the shell surface. External to this middle or prismatic layer is the epidermis or periostracum, the rough outer coating of varying shades, usually yellow or brown. Where the waves are rough, and the bottom hard and rocky, this covering is thick and heavy, to afford greater protection; but where the waters are smooth and gentle, and the bottom free from rocks, Nature—never working in vain—furnishes only thin sides and slight defense. As is the case with the nacre, the prismatic layer and the periostracum decrease in thickness from the hinge to the edge, and the inside lip of the shell shows the gradual union of the three superimposed layers. The two outer layers are formed by the thick edge of the mantle, the remaining portion—or nearly the entire surface—of this organ secretes the nacral layer.