1883. ] Pearls and Pearl Fisheries. 583 
head in the Fichtelgebirge. The Saxon fisheries are under the 
control of the Crown, through the ministry of the interior and of 
finance, and are chiefly located in the basin of the White Elster 
and its tributaries, upon which are situated twenty-eight mill 
reservoirs, 
The shell of the pearl mussel is composed of three layers; the 
outer brown or yellow conchioline or epidermis ; next a layer of 
prismatic character, the calcareous prisms being set at right angles 
to the inner surface of the shell, and lastly the inner layer of 
pearly or iridescent shell, which in the pearl oyster is called 
“mother-of-pearl.” The two latter layers are composed of car- 
bonate of lime, and at the margin the horny epidermis usually 
extends in a flap which is turned in over the edge but not at- 
tached to the inner surface. The mature shells sometimes reach 
six inches in length. 
If a foreign body, such as one of its own eggs, a grain of sand 
or a minute cercarian parasite penetrates where it irritates the 
mantle and ‘cannot be removed, it speedily becomes encysted or 
covered by a little capsule. This is thickened from time to time 
by additional deposits, and thus becomes a pearl. Upon the part 
of the mantle which makes the deposit, the character of the pearl 
depends. Some of the concretions partake of the nature of the 
epidermis, are brown and yellow and without luster. Most fresh- 
Water pearls, when sawed in two, exhibit an aggregation of the 
Prismatic shell substance radiating from a central point, which 
alternates with concentric epidermal layers and is externally cov- 
ered and adorned by a stratum of true pearl. If the last is thick, 
clear and iridescent, the pearl is valuable, if not, it is worthless. It 
is thus evident that the common notion of a pearl, as being pearly 
throughout, is in most cases incorrect. 
3 Disease may set up an irritation which will cause shelly concre- 
tions to form in the tissues of the mollusk. These are usually 
Small and irregular in shape, and in the pearl mussel are most fre- 
quent in the substance of the large muscles which close the valves. 
Such concretions are called sand-pearls, and are mostly used in 
embroidery and cheap jewelry. 
v In the above-mentioned cases the pearl lies in the substance of 
“le mantle or tissues, but it may happen that with increasing size 
it works out into the cavity of the shell outside of the mantle. 
In this case it is very apt to become attached to the inside of the 
