DIVISION II. MOLLUSCOUS AMIMALS.—CLASS IV. ACEPHALES. 
muscular contraction which closed them ceases to act. In many the folds 
of the mantle are quite open in front, as, for instance, in the oyster, 
which, on opening its shell, fully discloses its internal parts; in others 
they form a closed sack, with several openings —an anterior one for the 
passage of the foot, and two posterior ones for the ingress and egress of 
the water, which the animal requires for respiration. These posterior 
openings are often prolonged into shorter or longer tubes, sometimes 
separate, and sometimes grown together. 
The use or purpose of this formation becomes evident when we consider 
the mode of life of the animals thus endowed. Almost all of them live 
buried in the sand or mud, where they spend the whole or greater part of 
their life. Were their mantle open, they would inevitably be suffocated —a 
danger against which their long respiratory tubes, emerging into purer 
water, effectually protect them. Their strong muscular foot serves them 
as an excellent spade for rapid concealment in the sand, when an enemy 
approaches, and some species make use of it for creeping or hopping. 
The common cockle stretches it out as far as possible, presses it against 
the ground, springs up by suddenly contracting it, and hops rapidly along 
by quickly repeating the same manwuvre. In other species the movements 
are much more limited. Thus the Solenacea, or Razor-sheaths, content 
themselves with moving up and down in the vertical holes which they have 
dug, and which they never leave. 
Most of the siphonous bivalves inhabit sandy and muddy coasts in such 
vast numbers that the flat strand is often covered with their debris; but 
there are some which bury themselves in wood or stone. 
The Testaceous Mollusks are arranged in families, in the first of which 
is the genus 
Ostrea.— The Oyster. From its commercial value, and the rank it 
holds in our domestic economy, the Oyster may be styled the chief of the 
Molluscous animals. Although it is a universal favorite, and is consumed 
in immense quantities by all classes, our coasts appear to be capable of pro- 
ducing an inexhaustible supply. Its fecundity is extraordinary, a single 
oyster reproducing itself by a progeny of more than twelve hundred 
thousand. 
The Roman naturalist Pliny called the oyster “the palm or glory of 
the table,” and modern epicures will not question the excellence of his 
judgment. This valuable bivalve congregates in enormous banks, par- 
ticularly on rocky ground, though it is also found on a sandy or even a 
muddy bottom. In the tropical zone it frequently attaches itself to the 
roots and branches of the mangroves, and at ebb tide swings about as the 
wind agitates its movable support. It inhabits all the European seas as 
