OSTREA. 
as to throw it four or five inches at a time. In the 
water, an equal dexterity is evinced by the animal, 
in raising himself to the surface, directing his 
course ad libitum, and suddenly, by the shutting 
of his valves, dropping to the bottom. 
His less active relative, the rough Oyster, in the 
mean while, is contented to remain fixed to his 
first station, surrounded by an innumerable pro- 
geny, continually increasing with wonderful fecun- 
dity. His motions consist only in turning from 
one side to the other, which he accomplishes more 
by sagacity than any natural agility or inherent 
strength. He contrives to bolster up one side, by 
a gradual deposition of soft mud, till he stands 
nearly upright ; then, availing himself of the flow- 
ing or ebbing of the tide, he opens his shell, and 
is tumbled over by the pressure of the water. As 
expedition is not his object, this mode may answer 
well. 
It has, however, been observed that the young 
fry possess the power of swimming very swiftly by 
means of an undulatory motion of the branchiae. 
It is from the words oor^g/a or ocrr^sa, terms ap- 
plied generally to Bivalves by the Greek naturalists, 
that the Latin Ostrea and our Oyster are derived. 
