130 



THE OCEAN WORLD. 



Fig. 50. Another form of the Coral Polyp. 

 (Lacaze-Duthiers.) 



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 polyps 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 is their connection with the polypidom. 



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 polypidom. 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 polypidom. If the bark is examined more closely, 

 three principal elements are recognized a common general tissue, 

 some spicula, and certain vessels. The general tissue is transparent, 

 glossy, cellular, and contractile. 



The spiculse are very small calcareous concretions, more or less 

 elongated, covered with knotted joints bristling with spines, and of 

 regular determinate form (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 

 the fine colour which generally characterises it. 



The vessels constitute a network, which ex- 

 tends and repeats itself in the thickness of the crust. These vessels 



Fig 51 . Coralline SpicuU. 

 (Lacaze-Duthiers.) 



