THE POLYPS AND CORAL-MAKERS. 



35 



Before the embryo becomes fixed and the tentacles arise, 

 the lime destined to form the partitions begins to be de- 

 posited. Fig. 33, 6', shows the twelve rudimentary parti- 

 tions. These, after the young polyp has become stationary, 

 finally enlarge and become joined to the external walls of 

 the coral now in course of formation (Fig. 33, (7), form- 

 ing a foundation on which the polyp rests. D represents 

 the young polyp resting on the limestone pedestal, with 

 the tentacles well developed. 



But little is positively known as to the rate of growth of 



FIG. 33. Development of a coral polyp. A, ciliated gastrula; B, young polyp 

 with twelve partitions; C, />, young polyp farther advanced, with twelve 

 tentacles; C, the corallum and limestone septa beginning to form. (Magnified.) 



corals. A common brain-coral (\fa>Hdrina labyrinth ica), 

 measuring a foot in diameter and four inches thick in the 

 most convex part, attained its growth in twenty years. 



The common red coral (CoraUhon rubrum) of the Med- 

 iterranean Sea is worked into various ornaments. The 

 coral-fishery is pursued on the coasts of Algiers and Tu- 

 nis, where assemble in the winter and spring from two 

 hundred to three hundred vessels. The coral-fishermen, 

 with large rude nets, break off the coral from the sub- 

 merged rocks. About half a million dollars' worth of coral 

 is annually gathered. 



