136 REPORTS ON INVESTIGATIONS AND PROJECTS. 



only begun, but it is evident that the spermatophores, while exceptionally 

 large, are not so complicated as those of the squid. The spiral thread so 

 conspicuous in the ejaculatory apparatus of the squid spermatophore is much 

 reduced, the cement which forms so definite a part in the former is absent, 

 and there are other interesting and possibly important differences that will 

 receive attention later. 



Report of Investigations on Marine Bacteria carried on at Andros Island, 

 Bahamas, British West Indies, in May 1912, by G. Harold Drew, Cam- 

 bridge, England. 



The work described in this report was a continuation of that begun in 

 1911 at Port Royal, Jamaica, and at Tortugas. These former investigations 

 were summarized in the report of the Director of the Department of Marine 

 Biology of the Carnegie Institution of Washington for 1911, but in order 

 to make clear the objects of the present work it will be necessary to recapitu- 

 late briefly some of the chief conclusions arrived at in the former report. 

 In this it was shown : 



(i) That in the seas of the American tropics bacteria exist, which possess 

 the power of breaking down the nitrates in sea-water, first to nitrites, and 

 ultimately to free nitrogen. Traces of ammonia are formed in this process, 

 but the amount is never considerable ; it would seem probable that there is a 

 mutual decomposition between the ammonia and nitrites formed, giving rise 

 to the evolution of free nitrogen. In fluid culture media these bacteria 

 rapidly cause the complete destruction of nitrates which were contained in 

 the media, leaving no trace of either nitrate or nitrite. It was suggested 

 that the presence of these denitrifying bacteria, by keeping the nitrate con- 

 centration of the sea-water down to a minimum, would account for the rela- 

 tive scarcity of phyto-plankton in the tropics, and this in turn would account 

 for the scarcity of zoo-plankton, which ultimately depends on the phyto- 

 plankton for its food-supply. 



(2) That these denitrifying bacteria possess the power of precipitating 

 soluble calcium salts in the form of calcium carbonate from sea-water. It 

 was suggested that the thick deposits of fine chalky mud found in the Mar- 

 quesas Keys and in other places along the Florida coast are now being pre- 

 cipitated by bacterial agency, and that similar bacterial action may have 

 played an important part in the formation of chalk and other limestone rocks 

 in geologic times. 



The object of the work at Andros Island was to investigate the vertical 

 distribution of marine bacteria in the deep water of the Tongue of the 

 Ocean, and to study the bacterial flora of the immense flats of chalky mud 

 forming the shallows off the west coast of the island, with a view to obtain- 

 ing additional data as to the precipitation of calcium carbonate by bacterial 

 agency in the sea. 



The Tongue of the Ocean is a narrow strip of deep water, some 150 miles 

 long, entirely inclosed by land or shallows except at the northern end, where 

 it joins the New Providence Channel. The greater part of its western mar- 

 gin is formed by the coast of Andros, and it was at Golding Cay, at the 

 mouth of the South Bight of Andros, that the laboratory was established. 

 This position was especially suitable for the work, as by running out a few 

 miles in a direction at right angles to the coast-line the middle of the Tongue 

 of the Ocean could soon be reached, and also the mud flats to the west of the 

 island were readily accessible by water, as the South Bight runs right 



