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ARTICULATA. 
ORDER 11. CIRRHOPOBA. 
Cirrhopoda is derived from the Latin cirrus, a lock of hair, and tlie Greek pous, a foot. These, 
until recently arranged with the mollusca, are all mariiae 
animals, which, when mature, attach themselves to rocks or 
other submarine objects. The Common Barnacle, Lepas 
anatifera, perhaps the best-known example of the order, gen- 
erally selects floating objects for this purpose, and frequently 
covers the bottoms of ships to such an extent as even to 
impede their progress through the water. It adheres by a 
flexible stalk, which possesses great contractile power. The 
shell is usually composed of two triangular pieces on each 
side, and is closed by another elongated piece at the back, 
so that the whole consists of five pieces. The Anatifa 
anserifera of De Kay, and other species, are found on ships' 
bottoms at New York and other places in America. The 
S Sea- Acorns, or Balanidce, include the sessile species, whose 
curious little habitations may constantly be met with upon 
the rocks of the sea-shore, and not unfrequently upon many 
BARNACLES. spccics of mariuc shells. There are several American species. 
These animals, called Wheel Animalcules, were formerly included among the Infusoria, but are 
now classed with the Articulata : they are chiefly known to us by the microscope, the largest 
being not over a tenth of an inch long, and many of them only one three-hundredth 
of an inch. They inhabit both salt and fresh water, and are distributed over nearly 
all parts of the world. They are not only numerous beyond all human conception, 
but they are divided into over fifty genera and two hundred species. Notwithstand- 
ing their minuteness, the careful studies of naturalists have made us acquainted with 
their structure and habits. They are generally of an elongated form, though some are 
nearly as wide as they are long. They are each provided with a rotatory organ, 
called a wheel, which consists of retractile fleshy lobes, covered with vibrating cilia, 
placed at the anterior extremity. By an apparently circular movement of these 
organs they produce a whirling vortex in the water, which brings to their mouths 
any minute animals which may be floating in the neighborhood. By this ingenious 
but curious contrivance these creatures obtain their food. 
It has been ascertained that they have a complicated muscular system, a stomach, 
and a nervous system ; they are true hermaphrodites, and possess amazing power of 
reproduction, Ehrenberg states that in three days the progeny of a single specimen 
of Hyclatina senta, which he had separated, amounted to no less than twenty indi- 
viduals, a rate of increase which in ten days would produce more than a million of 
specimens. He adds that " if two, instead of four, were produced daily by each indi- 
vidual, a million would be called into existence in twenty days, and on the twenty- 
fourth day we should have sixteen millions seven hundred and seventy-seven thousand 
two hundred and sixteen animalcules!" But astonishing as is this increase, there 
is another fact equally wonderful, which is, that though these creatures only show life in water, 
they will revive after having long remained dried up with the sand. Professor Owen asserts that 
WHEEL 
ANIMALCULE, 
