THE 
AMERICAN NATURALIST. 
VoL. xviu.— FUNE, 1883.—No. 6. 
PEARLS AND PEARL FISHERIES} 
BY W. H. DALL. 
Part I. 
pie beautiful objects which form the subject of this discourse 
are familiar to all, and though neither gems nor jewels they 
are generally associated with them in our minds and put to simi- 
lar uses in fact. No gem in its natural condition will compare 
for a moment in beauty with the perfect pearl, as nature offers it; 
any touch except that necessary to fasten it in its setting would be 
desecration, On the other hand true gems, except the opal which 
comes nearest to the pearl, in general owe their attractiveness 
far more to the manner in which they are cut and polished than 
to their inherent properties, 
Pearls are produced by shell fish, or, more precisely, by certain 
mollusks inhabiting the water, the inner layer of whose shells 
Possesses the same iridescent or nacreous character, and is often 
known as “ mother-of-pearl.” 
The soft internal part of these creatures is covered by a thin 
delicate membrane called the mantle, by the surface and especially 
the outer edge of which the shell is secreted. The shell consists 
t two parts, the epidermis and the shelly matter proper ; the lat- 
ter, again, is usually composed of more or less different layers. 
The epidermis or skin is of a horny texture and chiefly composed 
se: a substance called conchioline. It is usually colored darker 
| k Sieg brown, and may be extremely thin or almost invisible. 
_ “May be entirely dissolved in caustic alkali, but is not affected 
Aras delivered at the National Museum, Washington, at the request of the 
ee of the Biological and Anthropological Societies. 
VOL, XVII.—No. vr, 40 
