1 18 F'ossil Corals, — Lower Silurian Roch of Canada. 



Hydra from the raouth, we should have an approximate idea of the struc- 

 ture of what is improperly called the coral insect. The bodies of most of 

 these consist of two sacks, one within the other, the mouth communicating 

 only with the smaller or inner sack. The space within, all round between 

 the two sacks, is divided by a number of upright partitions which extend 

 from without inwards. As in the Hydra, there are no viscera. The food is 

 captured by the tentacula, and drawn into the stomach through the mouth 

 passing first into the inner sack vrhere it is digested. The undigested por- 

 tions are then thrown out through the mouth, but the liquid extracted from 

 the food is discharged through an aperture at the bottom of the inner sack 

 and flows into the space between the two, Avhence it is absorbed into the 

 general structure of the animal, as in the Hydra. 



The above explains the leading features of the structure of those Polypi, 

 whose secretions form lara-e areas of submarine rock in manv of the warmer 

 regions of the ocean. Those who wish to pursue the subject farther, and 

 we strongly recommend all who feel any interest in the wondrous works of 

 the Creator to do so, must consult other books where these matters are 

 treated of more in detail. 



The Hydra, and a multitude of the other Polypi, are entirely soft, and 

 do not form coral ; but in great many other genera, within the substance of 

 the outer wall or sack, and also of the radiating partitions, various stony 

 elements are secreted, and an internal hard skeleton is formed. As the 

 animal is attached to the rock, so is its skeleton, and as when one generation 

 dies another grows upon its remains, so the reef must grow until it reaches* 

 the surface of the water, and thus those obstructions to the navigation so 

 common in many of the seas are produced. 



The corals grow upon the bottom of the ocean in a great variety of 

 forms. Some of them spread over the rock in an incrusting layer, consisting 

 of m}Taids of the Polypi, connected together and forming a continuous thin 

 sheet over the bottom everywhere alive with their minute flower-like forms. 

 Others sprout upward in the shape of shrubs or small trees, with stout round 

 branches, each formed of thousands of the Polypi : while some species fonn 

 little rounded hillocks, like the dome of a Turkish Mosque, and in size from 

 two or three inches to twenty feet in diameter. The Polyps spread over 

 these with their circles of tentacula, appear like so many individual flowers, 

 and they are moreover so radiant with colours, that, according to the descrip- 

 tions of travellers, no scene upon earth is more beautiful than one of those 

 submarine gardens. * 



* Among them, says Professor Dana, are flowers of all hues and sizes. The 

 Actiniae may be well called the Asters, Carnations, and Anenionies of the submarine 

 garden; the Tubipores and Alcyonia, form literally its pink beds; the Gorsronia 

 and Melitfeos, are its flowering' twigs ; the Madrepores, its plants and shrubbery ; 

 and Astrceas often form domes amid the grove, a dozen feet or more in diameter, 

 embellished with green or purple blossoms which stud the surface like gems ; whil« 

 other hemispheres of Meandriua appear as if enveloped in a net-work of flowerins; 

 vinea- 



