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IV
STRUCTURE AND FORMS OF PEARLS
"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.
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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
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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 laminae 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 de-
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