124 COEAL BANKS. 



beautiful kinds, ornamented with all the colours of 

 the rainbow. 



The internal structure of the Sea Anemone is very 

 curious. The Polypes of the Hydroida are exceedingly 

 simple in structure, their flesh being composed of a 

 homogeneous mass of cells, heaped together, and formed 

 into a bag-like body. In these Helianthoida the struc- 

 ture is much more compound : there is an outer leathery 

 skin, separated from the inner coat or wall of the 

 stomach by a hollow space, in which are placed numer- 

 ous vertical partitions or lamiuso, radiating towards the 

 centre like the gills of a mushroom. These plates have 

 their origin on the inner surface of the leathery coat, 

 to which they act as a support ; some of them project so 

 far as to touch the walls of the stomach, and others are 

 narrower and shorter than the rest, exactly as we find the 

 gills of a mushroom. A similar structure is found re- 

 presented in stone, in the well-known Mushroom Coral or 

 Madrepore of our cabinets, which is indeed the skeleton 

 of an animal closely allied to the Sea Anemone. In the 

 Sea Anemone, the laminae continue fleshy during the life 

 of the animal; in the Madrepore they secrete a coating 

 of carbonate of lime, which thickens by degrees, and at 

 length forms a stony cast of the animal. The lower parts 

 gradually die away, as the stony matter increases, while 

 the Polype-body, continuing to live, is pushed upwards, 

 and thus the Corals of this family are produced. In the 

 seas of tropical and subtropical countries, the species of 

 Calcareous Corals of the Helianthoid order are exceed- 

 ingly numerous, and their office in the natural economy 

 most wonderful Ceaselessly, from the earliest ages of 



