182 CARNEGIE INSTITUTION OF WASHINGTON. 



being soon covered with scar tissue which in time develops polypites 

 over its surface. 



Dr. Hubert Lyman Clark made a detailed study of the growth- 

 changes in brittle-stars, Ophiothrix, Ophiactis, and Amphipholis. His 

 conclusions being based on the observation that as the terminal seg- 

 ments of the arms of these star-fishes are the youngest, they may be 

 expected to reveal the developmental stages through which the arm 

 has passed. He calls attention to the fact that the genetic relation- 

 ships of ophiurans can be determined only when we know the history 

 of the changes in appearance and structure of their skeletal plates and 

 organs during growth from the young to the adult stage. 



Mr. R. B. Dole analyzed a series of samples of the lagoon water of 

 the Tortugas atoll which had been collected throughout a lunar month, 

 at all stages of the tide, by Dr. T. Wayland Vaughan. Mr. Dole con- 

 cluded that there is no free carbon dioxide either in the Tortugas 

 lagoon or in the surface-waters of the ocean surrounding the islands, and 

 that the sea-water has no power to dissolve limestone by virtue of its 

 content of carbon dioxide. Should this conclusion be confirmed, it is 

 one of primary importance from a geologic standpoint, for it would 

 indicate that solution has had no part in the formation of the lagoons 

 of coral atolls and barrier reefs. 



An important research was conducted by the late George Harold 

 Drew, of Cambridge University, England. Dall was the first to assert, 

 and Sanford and afterward Vaughan concluded, that the finely divided 

 limestone mud of the lagoons and sounds of southern Florida was a 

 chemical precipitate. The cause of the precipitation remained a 

 mystery, however, until Drew discovered that there is in the surface 

 waters of the Florida- West Indian region a very abundant bacillus 

 which, if grown in sea-water containing calcium malate or calcium 

 succinate in the presence of a nitrate, changes the nitrate into nitrite 

 and finally causes nitrogen to be set free and to escape from the solu- 

 tion. Drew concluded that this reaction must cause a precipitation of 

 calcium carbonate in the sea-water. After Drew's death. Dr. Karl F. 

 Kellerman studied this process and found that Drew's bacillus did not 

 produce a precipitate of calcium carbonate in pure sea-water unless 

 free carbon dioxide was present, and he concluded as a result of further 

 experiments that calcium carbonate is precipitated from ocean-water 

 if an anamonium-producing or a denitrifying organism is grown in asso- 

 ciation with one which produces carbon dioxide. 



As a result of these studies, we now know that limestone is con- 

 stantly being precipitated to form the impalpable mud of the Bahama 

 banks and Florida lagoons, and, moreover, the conclusions of Brandt 

 are confirmed, that the relative paucity of plant life in tropical oceans 

 (and consequently the scarcity of animal life), is due to the relative 

 lack of nitrogen in warm seas. 



