132 
THE OCEAN WORLD. 
A cylindrical tube connected with the mouth represents the oeso- 
phagus or gullet ; but all other portions of the digestive tube are very 
rudimentary. The oesophagus 
connects the general cavity of 
the body with the exterior, and 
looks as if it were suspended in 
the middle of the body by certain 
folds, which issue with perfect 
symmetry from eight points of 
its circumference. The folds 
which thus fix the oesophagus 
form a series of cells, above each 
of which it attaches itself, and 
supports an arm or tentaculum. 
Let us pause an instant over 
the soft and fleshy bark in which the polypes are engaged. Let us 
see also what are the mutual relations which exist between the several 
inhabitants of one of these colonies, how they are attached to one 
another, and what their connection with the polypier. 
The thick fleshy body, soft, and easily impressed with the finger, is 
the living part which produces the coral ; it extends itself so as ex- 
actly to cover the whole polypier. If it perishes at any one point, that 
part of the axis which corresponds with the point no longer shows any 
increase. An intimate relation, therefore, exists between the bark and 
the polypier. If the bark is examined more closely, three principal 
elements are recognised — a common general tissue, some spicula, and 
certain vessels. The general tissue is transparent, glossy, cellular, and 
contractile. 
The spieulse are very small calcareous concretions, more or less 
elongated, covered with knotted joints bristling with spines, and of 
regular determinate lbrm (Fig. 51). They refract 
the light very vividly, and their colour is that of 
the coral, but much weaker in consequence of 
their want of thickness. They are uniformly dis- 
tributed throughout the bark, and give to the coral 
1& (nac^DuMerso U ' a the ^ ne c °l° lir which generally characterises it. 
The vessels constitute a net-work, which ex- 
tends and repeats itself in the thickness of the crust. These vessels 
Fig. 50. Auotlier form nf the Coral Polype. 
(Locuste- 1 luthiers.) 
