ORDERACTINOIDEA. 83 



the polyp forms an ascending stem, either cylindrical or turbinate. 

 Branching takes place (n] either by lateral shoots, as in the Caryo- 

 phyllise, or (o) by subdivision or furcation at apex, as in the Mussse, 

 Euphyllise, &c. ; and the coralla of these species are, in both in- 

 stances, styled caliculato-ramose. When (p) the branches are laterally 

 in contact, as in the Columnarise, or are united transversely at inter- 

 vals, as in the Tubipores, fasciculate forms result. 



83. We thus perceive the principal steps by which corals take on 

 their specific forms, and see reason for the fact that these forms are con- 

 stant in the same species. The many varied shapes of zoophytes, the 

 tree, the shrub, the clustered leaves, globes and hemispheres, clubs, 

 twigs, and coral network, require for their explanation only the few 

 principles here adduced. The germ-polyp, growing upward and 

 budding as it grows, gives rise to the various branching and nodular 

 zoophytes, while by growth laterally, the explanate or oblique foliated 

 species originate. In the upward mode of growth, when all the 

 polyps bud equally, globes and hemispheres are produced ; but if the 

 gemmating power is retained only by the recent polyps, the zoophyte 

 lengthens into stems and cylinders. When, in this last process, 

 budding takes place symmetrically, the zoophyte is erect; if unsym- 

 metrical, it is oblique or horizontal ; and the zoophyte, when erect, is 

 cylindrical or a flattened plate, according as buds form alike on all 

 sides of a centre, or open in two opposite directions. In some acro- 

 genous species, there is a terminal polyp, parent-polyp, from which 

 the buds proceed; in others, a terminal cluster of polyps. The former, 

 ramify by lateral shoots, common polyps changing to parent-polyps, 

 and thus becoming the germs of branches, which take their direction 

 from the position of the budding-polyp ; the latter, branch generally 

 by furcation at summit, the size of the terminal cluster determining 

 the diameter of the branch, and indirectly occasioning the furcation. 



In other species still, each polyp gives out its single polyp in suc- 

 cession, and the continued accumulation produces the rising stem, 

 which ramifies either by the processes just mentioned, or from buds 

 at apex, forming periodically and becoming the germs of branches. 



There is much to surprise and interest us in tracing out the simple 

 causes of results so remarkable. The small polyp, incapable even of 

 extending its arms without a drop of water to inject them, is enabled, 

 by means of a simple secretion in its texture, in connexion with the 

 process of budding, to rise from the rock and spread wide its branches, 

 or erect, with solid masonry, the coral domes, in defiance of the waves 



