82 POPULAR HISTOllY OF THE AQUARIUM. 



to cling firmly to rocks and other surfaces; while amid 

 boisterous tempests agitating the waters^ his extended body 

 bends to the waves, and his many arms are active in search 

 of food. The edge of the outer covering will be distin- 

 guished by a darker colour and more opaque texture, from 

 the rest of the disc. From it, radiating towards a common 

 centre, are opaque white lines ; some reaching the centre, 

 and others, shorter, between them. If at any height in the 

 body of the animal a cross section be made, these same lines 

 will appear ; showing them to be edges of vertical plates, of 

 a different substance from the rest of the body. The spaces 

 between these plates and the central stomach are filled up 

 with translucid jelly-like flesh, which is capable of being 

 greatly swelled with water. If a section were made of a 

 Single-starred Madrepore, such as Caryojphyllea Smithiiy or 

 the Mushroom Coral of the Pacific, the same arrangement of 

 radiating plates would be observed ; only in these instances 

 they are hard and calcareous, — in short, coral ; while in 

 Actinia they are only a kind of gristle, and, being of a 

 firmer texture than the flesh, give support and firmness to 

 it. This is the essential difference between Actinice and 

 Single-star Corals. The latter however are fixed, while the 

 former, as we have seen, are locomotive. 



