On the Economical Uses of some species of Testacea. 61 
ents. ‘The Byssus is of a dark green color and metallic hue, and 
they can move slightly by contracting or extending the muscle to 
which it is attached. The ancients supposed them to be endowed 
with peculiar powers of locomotion, describing them as grazing at 
the bottom of the ocean, with a leader to direct them, &c.* but 
whether they have any such power is extremely doubtful, at least 
after attaining the thick shell.t The sexual differences have not 
hitherto been discovered, although the natives of Ceylon pretend to 
distinguish the sexes, by the appearance of the shell. ‘Those that 
are large and flat, they call males; those that are thick, concave and 
vaulted, they call females; but Mr. Le Beck, who appears to have 
carefully examined and dissected this animal, declares he was una- 
ble to discover any difference. 
Like the Ostrea edulis, this fish appears to thrive best. in a mix- 
ture of fresh and salt water. Pearls are always the most beautiful 
in those places of the sea where a quantity of fresh water falls, as at 
the mouth of rivers and streams,{l while those produced by the shells 
growing on rocky bottoms, are found to be of a better water than 
those that lie among sand and coral. 
Of the many suppositions as to the cause of pearls, that of Rau- 
meur is the most probable, and in the present day generally adopt- 
ed. He supposed them to be owing to a disease in the fish, as c 
culi in mammalia, and to arise from a’ruptured or morbid state of the 
vessels provided for the secretion of the materials of the shell: most 
experiments and observations go to prove the truth of it.]| 
* Pliny, rx. 35. “ 
Mr. Montgomery M kes the fi ks on this shell, but from 
his very obvious ignoran ce of natural entities id the i 
haste of his observations in this department, they are very little to be relied on 
We however give them, as from a modern and widely circulated work, and not 
tirely without its merits, although abounding in faults. “ At certain seasons, 
the young oysters are seen floating in masses, and are carried by the currents 
round the coasts (of Ceylon.) ‘They afterwards settie and attach themselves by a 
fibre or beard on coral rocks, and on-sand; they adhere together in clusters; when 
full grown, they again separate, and beconie locomotive. The pearls ores dur- 
ing six years, and the oyster is supposed to die after seven — ”"—Martyn’s His- 
tory of the British Colonies, 2d ed. I, 522, note. 
t Asiatic Researches, ut supra. Dr. Kirtland remarks the same with respect to 
those species of the family of “Natades of Lamarck, which are found in the waters 
of this country, and he is “persuaded that each sex possesses a peculiar organiza- 
tion of na associated with a corresponding form of the shell, sufficiently well 
: o distinguish it from the other.”—Silliman’s Arieticnn Journal, Vol. 
his 118, 119. 
7 Bruce’s Travels to discover the Sources of the Nile, VIL. 322. 
| Transactions of the French Academy 
