94 CORALS AND CORAL ISLANDS. 



number of species, and gives an excellent idea of the most of 

 the forms of Actiniae, and also presents well their colors. 

 Prof. A. E. Verrill has published, in the Memoirs of the Bos- 

 ton Society of Natural History, Vol. I., a " Review of the 

 Polyps of the Eastern Coast of the United States," with a 

 plate illustrating a few of the species. 



IV. LIFE AND DEATH IN CONCURRENT PROGRESS IN CORAL 



ZOOPHYTES. 



The large, massive forms of stony corals would not exist, 

 and the tree-shaped and other kinds would be of diminutive size, 

 were it not for the fact that, in the living zoophyte, death and 

 life are going on together, pari passu. This condition of 

 growth is favored by the coral secretions ; for these give a 

 chance for the polyp to mount upward on the coral, as it 

 lengthens it by secretions at the top. But, to be successful in 

 this ascending process, either the polyp must have the power 

 of indefinite elongation, or it must desert the lower part of 

 the corallum as growth goes forward ; and this last is what 

 happens. In some instances, a polyp, but a fourth of an inch 

 long, or even shorter, is finally found at the top of a stem 

 many inches in height. The following figure represents a case 

 of this kind; for all is dead coral, excepting less than an 

 inch at the extremity of each branch. The tissues that once 

 filled the cells of the rest of the corallum have dried away, 

 as increase went on above. Another example is shown 

 on page 54, in which the living part had a length of one 

 eighth of an inch. The Goniopora, on page 52, is still an- 

 other example of the process ; but here the living part com- 

 bines a great number of polyps : these are growing and bud- 

 ding with all the exuberance of life, while below, the old pol- 



