70 CORALS AND CORAL ISLANDS. 



pinnules or processes along it (the Virgularidse) ; or a thin 

 reniform shape (Renillidae). Others differ from the preceding 

 in having the polyps not retractile ; and some of these have a 

 slender stem and the polyps arranged along one side of it 

 (the Pavonaridae) ; and still others a terminal cluster of polyps 

 (the Umbellularidce). 



The most of the species secrete a slender, horny axis, and 

 have slender calcareous spicules among the tissues, somewhat 

 like those of the Gorgonidje. 



In conclusion, it may here be stated that the reader will find 

 very full illustrations of most of the forms of recent corals, 

 and of their animals, with their natural colours, in the author's 

 Report on Zoophytes. It is with regret that he has to add, 

 that owing to the special action of the Congressional Commit- 

 tee in charge of the publications of the Wilkes Exploring 

 Expedition, only one hundred copies of this Report were pub- 

 lished by the Government, and also of the others of the series, 

 and that but i^\N have been issued besides. The Atlas contains 

 sixty-one folio plates, many of them coloured. 



The works on " British Sea Anemones," by Mr. Philip 

 Henry Gosse, contains figures and descriptions of a large 

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

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

 Professor A. E. Verrill has published, in the Memoirs of the 

 Boston 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 favoured by the coral secretions ; for these give a 



