GENERAL ZOOLOGY. 75 



rather were formed as promontories of pre-existing higher lands, con- 

 tiguous to great bays of the ocean." 



" Subsequent to this period, the formation of coral reefs took place only 

 in particular localities, as we find it at the present day. The Tertiary 

 period presents no more vast calcareous formations of coral purely ; the 

 function of the coral animals in depositing lime has become more of a local 

 nature, confined to some favourable situations ; while the secretion of lime 

 by the Polythalamia, an agency which was wholly unknown at the earliest 

 epoch, assumes a more and more predominant influence in the formation of 

 the surface of the globe, as we approach the present times. The Nummulite 

 limestone of the Mediterranean beach, the Calcaire Grossier of the Paris basin, 

 the Molasse of Switzerland, and the sub-Appenine limestones, are composed 

 almost entirely of the shells of these minute, but tough creatures, whose 

 indefatigable industry has furnished one of the best and most important of 

 building materials for the use of man. Almost the whole of Paris is con- 

 structed of the shells of Foraminifera, and the material of the Egyptian 

 pyramids themselves is a limestone, accumulated ages ago, of countless 

 millions of Nummulites." 



" I have now, my friend, set before you, as I consider, the most essential 

 and interesting facts in the Natural History of the Polyps ; but you may 

 still be curious to know on what the little creatures live, as this has not 

 been mentioned yet, although their alimentary organs have been described 

 before. There can be no doubt that their chief food consists of living 

 animals, and that the Polyps, in general, swallow these whole, having 

 drawn them within their reach by means of the current created in the 

 water by their cilia, or having caught and benumbed them with their sting- 

 ing lines. This may be easily verified in the freshwater Hydra. The 

 stomach, in most of the marine Polyps, is generally found empty, and 

 seldom filled with any large bodies. They must be able to endure long 

 abstinence, and content with small particles of food. What means, indeed, 

 have they to master the larger animalcules ? The current which they 

 create, their chief means of obtaining aliment, is too feeble to overpower 

 those of any bulk, neither are their tentacles long enough to reach and 

 envelope such. Vegetable matter does not seem to enter into their alimen- 

 tary cavity, probably because it is not fit for their sustenance. There are, 

 indeed, plants floating freely in the sea, but this only in a few situations, 

 and these are far too bulky to be swallowed by a Polyp, while it has no 

 organs with which to detach from them smaller portions. A Polyp cannot 



