Coral Builders. 45 



are solitary ; a few only form colonies by continuous 

 budding, and by the formation of a uniting crenosarc. 

 In sea anemones proper, there is no deposition of an 

 indurating material, but in tropical seas there are 

 closely allied animals which abstract lime from the 

 sea-water, and lay it down in one of two ways, either 

 in the animal's tissues, or else in the centre of the 

 ccenosarc, and around the body, outside the foot of 

 each separate polyp. Hard masses thus formed 

 are called corals ; and all the reef-building corals, the 

 Madrepores and Oculinas, are examples of the former 

 kind, or tissue-depositions. The deposit may be 

 in the body wall, in the mesenteries of the polyps, 

 or in the coenosarc. Growth in these colonial forms 

 takes place either by the formation of buds which 

 remain continuous and may spring from various 

 parts of the original stem, or else by fission, but in 

 this case the new polyps remain connected together. 

 Owing to these different modes of growth there 

 is much variety of shape and structure among the 

 hard parts of different corals. Large masses of coral, 

 which are called reefs, are usually found in the seas 

 of such climates as have a winter average tem- 

 perature over 60 F. and where the water is clear, 

 and not mixed with mud or fresh water. They 

 abound chiefly between the depths of i and 50 

 fathoms, and vary in form according to the shape and 

 condition of the sea-bottom. 



A few of the coral-building animals are solitary, 

 like the little Caryophyllia of our own seas. Some 

 of the commonest forms of corals brought to this 

 country from the tropics are the mushroom-shaped 



