23O THE OCEAN WORLD. 



Let us pause an instant over the soft and fleshy bark in which 

 the polyps are immersed. 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 

 exactly 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 recognised a common general 

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

 transparent, glossy, cellular, and contractile. 



The spicules are very small calcareous bodies, more or less 

 elongated, covered with knotted protuberances 

 bristling with spines, and of a more or less 

 regular determinate form (Fig. 87). They refract 

 the light very vividly, and their colour is that of 

 the coral, but much less vivid, in consequence 

 of their want of thickness. They are uniformly 

 Fig. 8 7 .-Corai Spicules Distributed throughout the bark, and give to the 

 (Lacaze-Duthiers). coral the fine colour which generally characterises 



it when in a living state. 



The vessels constitute a network, which extends and repeats 

 itself in the thickest of the bark. These vessels are of two kinds 

 (Fig. 88) ; the one, comparatively very large, is imbedded in the 

 axis, and disposed in parallel layers; the others are regular and much 

 smaller. They form a network of unequal meshes, which occupies 

 the whole thickness of the external crust. This network has direct 

 and important connection with the polyps on the one hand, and with 

 the central substance which forms the axis on the other. It com- 

 municates directly with the general cavity of the body of the animal, 

 by every channel which approaches it, while the two ranges of net- 

 work approach each other by a greater number of anastomosing 

 processes. Such is the vascular arrangement of the coral. 



The circulation of alimentary fluids in the coral is accomplished 

 by means of vessels near to the axis, without, however, directly 

 anastomosing with the cavities containing the polyps which live in 

 the polypidom ; they only communicate with these cavities by very 

 delicate intermediary canals. The alimentary fluids they receive 

 from the secondary system of network, which brings them into direct 



