100 THE WORLD OF THE SEA. 
yellow, and some appie green ; in some the tints pass from olive- 
brown to dark blue, from vermillion to violet, and from pale 
yellow to pearly grey. Each tube or cell contains a polype, its 
depth varying in the several species. The animals are composed 
of two parts, one which remains in the cell, and the other is the 
starry termination which is visible; from the latter radiate eight or 
twelve projecting arms, sometimes quite soft and pliable, at other 
times granular. They can expand themselves like the petals of a 
blossoming flower, and when outspread, their length is often greater 
than that of the whole body of the polype; they are transparent, 
save just at the tips. The polypes extend or contract their feelers, 
TUBIPORINE, OR MUSICAL CORAL, 
(Tubipora musica.) 
and open and shut their mouths at will, but their digestive tube 
is fastened to the walls of the cell, and the stem, upon which 
the cells are built, is condemned to immovability. Thus, although 
they can put their heads out of the door of their houses, yet they 
can never leave home. Their life is spent in moving about their 
arms to produce currents in the water, which bear to them the food 
they need; while their digestive apparatus separates from the 
water, as it passes through the stomach, the lime it contains, of 
which they construct their tube. The coral polypes thus present 
hard, insensible, stony matter, built up by 
a singular combination 
and indissolubly joined to a living creature. 
The animalcules of the polypiers are propagated by larve 
or by buds developed from the cortex of the parent. In 
the hydra polypes the eggs are contained in special horny 
capsules, which break as soon as the germs reach their maturity. 
