220 THE OCEAN 



organisms must be able to utilise the other 

 salts of calcium present in sea-water in the 

 formation of the carbonate. Wherever effete 

 animal matter is thrown into the sea, or 

 wherever animal structures are undergoing 

 decay in the ocean, decomposition-products, 

 many of them of a complex constitution, 

 pass into solution. In the presence of sea- 

 v/ater salts these products give rise to many 

 reactions, the formation of ammoniacal salts 

 always taking place to a greater or less extent. 

 Carbonate of ammonia, arising from the 

 decomposition of animal products, in presence 

 of the sulphate of lime in sea- water becomes 

 carbonate of lime and sulphate of ammonia. 

 The whole of the lime salts in sea-water 

 may be changed by this reaction into car- 

 bonate, and so presented to the lime-secreting 

 organisms in a form suitable for their re- 

 quirements. Murray and Irvine's well-known 

 experiments with crabs and hens seem to 

 point conclusively to this origin of calcareous 

 structures in the living animal. The tempera- 

 ture of the water is of great importance in this 

 reaction, which is retarded in cold water but 

 proceeds with great rapidity in warm water. 

 This probably explains the great development 

 of massive calcareous structures in the coral 

 reef regions, which are also the regions of 

 highest and most uniform temperature in the 



