On Coral Reefs and Islands, 165 



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4A 



Art. XIX. — On Coral Reefs and Islands ; by James D. Dana. 



Part Third. 



From the Report on Geology of the Exploring Expedition under Capt. Wilkes, F.S.K 



StkucturEj Growth, and Habits of Coral Zoophytes, 



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1. Structure and Growth of Zoophytes. 



A SINGULAR degree of obscurity has been thrown around the 

 growth of coral zoophytes and coral formations, through the va- 

 rious speculations which have been offered in place of facts; and 

 to the present day, the subject is seldom mentioned without the 

 qnahfying adjective mi/slerious expressed or understood. Some 

 writers, scouting the idea that reefs of rocks can be due in any 

 way to "animalcules/' talk of electrical forces, the first and last 

 appeal of ignorance. Others call in the fishes of the seas, sug- 

 gesting that they are the masons, and work with their teeth in 

 the accumulation of the calcareous material. Very many of 

 those who discourse quite learnedly on zoophytes and reefs, im- 

 ^gnie that the polyps are mechanical workers, heaping up these 

 piles of rock by their united labors; and science still retains 

 such terms as polypary, polypidom, as if each coral were the 

 constructed hive or house of a swarm of polyps, like the honey- 

 comb of the bee, or the hillock of a colony of ants. 



It is vain to hope to understand fully the works of Him who 

 '^s himself infinite and incomprehensible. The scrutinizing eye 

 of science penetrates with far-reaching sight the system of things 

 >ibout us, and in the dim limits of vision reads everywhere the 

 word mystery. All life, animal and vegetable, and all that is in- 

 animate, declare it; surely there is no special reason, except such 

 as niay arise from want of study and consideration, for attribut- 

 uig it pre-eminently to the humblest grades of existence. 



It is not more surprising nor a matter of more difficult com- 

 prehension that the polyp should form coral, than that the quad- 

 ruped should form its bones, or the mollusc its shell. The pro- 

 cesses are similar, and so the result: in each case it is a simple 

 animal secretion, a formation of stony matter from the aliment 

 which the animal receives, produced by certain parts of the ani- 

 raal fitted for this secreting process. This power of secretion is 

 the first and most common of those that belong to living tissues; 

 and though differing in different organs according to their end or 

 itiuction, it is all one process, both in nature or cause, whether 

 "J the animalcule or in man. Coral is never, therefore, an ag- 

 ghuination of grains made by the handywork of the many- 

 armed polyps : for it is no more an act of labor than bone-mak- 

 ^"g in ourselves. And again, it is not a collection of cells into 



