DEPARTMENT OF MARINE BIOLOGY. 



165 



flagellates, or ciliates were present in any of the bottles, showing that the 

 method of sterilization employed in these experiments is reliable. 



Table shotving distribution of amebas at Tortugas. 



These experiments were designed to test the abundance of amebas (or 

 cysts) in all the general regions of the Tortugas Keys, in the surface water of 

 the Gulf Stream near the shore and far out, and on floating Sargassum. The 

 results as a whole show that the method adopted is generally satisfactory for 

 determining the distribution of amebas. 



The results of experiments 3, 4, and 11, comprising 307 cultures, of which 

 14 bottles contained amebas, show that the surface water of the Gulf Stream in 

 the Tortugas region contains about 4.56 amebas per 10,000 c.c. of water. 

 Experiments 1, 4, and 6 show that amebas are much more abundant on a solid 

 support. Experiments 8, 9, 10, and 11 show that amebas may exist for 

 considerable periods in the encysted stage exposed to tropical sunlight. 

 Flahellula mira forms cysts, but F. citata apparently does not. The distribu- 

 tion of ciliates corresponds roughly to the distribution of amebas in the 

 cultures. Since the amebas in question and the ciliates feed on bacteria, 

 it is probable that this correspondence is further proof that the distribution 

 of amebas as well as of ciliates is conditioned by the presence of comparatively 

 rich bacteria cultures. 



F. mira has come up much more frequently than F. citata, and yet in 

 previous years both at Tortugas and at Cold Spring Harbor, New York, 

 F. citata nearly always came up in enormous numbers, in large mass cultures 

 of various kinds of algse selected at random. No explanation for these appar- 

 ently conflicting observations can yet be given. 



