DEPARTMENT OF MARINE BIOLOGY. 205 



data obtained in other localities. But some observations have been made 

 which indicate that the problem of distribution is a practical one to investigate. 

 It has already been noted, for example, that several species of amcebas found 

 on floating sargassum from the Gulf Stream were not found on the seaweeds 

 growing near the shore-hne. More important in this connection is the fact 

 that 4 of the 5 amcebas described feed principally on bacteria, and they con- 

 sequently occur most abundantly where vegetative or animal matter is under- 

 going disintegration. These species are therefore distributed, at least to 

 some degree, in accordance with the quantitative distribution of bacteria. 

 Another observation of importance in the study of distribution is the degree 

 of resistance which different species of amoebas show toward varying con- 

 centrations of the salt-content of sea-water. Two of the species described 

 are resistant to inunersion in fresh water for a considerable period of time 

 (10 minutes), while another species loses all power of movement in 50 per cent 

 sea-water and dies in 25 per cent sea-water. The former two species evidently 

 may live in brackish water, while the latter species can not. Again, one of the 

 species can Hve and move in concentrated (364 per cent) sea- water as well as in 

 fresh water, while other species shrivel up and disintegrate in such highly con- 

 centrated water. The former species may therefore conceivably live in some 

 inland seas whose waters contain a high percentage of salt, while other species 

 seem to be more or less closely adjusted to the amount of salt found in the 

 water of the ocean. The species that can withstand fresh water as well as 

 364 per cent sea-water might therefore be expected to be found living in fresh 

 water occasionally in natural conditions. Such does not seem to be the case, 

 however, for this species has never been reported from fresh water. In fact, 

 no species of amoeba is known that Hves naturally both in fresh and salt 

 water. The distribution of amoebas over the world appears, therefore, to be 

 determined by a number of factors. 



The difference various species of amoebas show in their resistance to sea- 

 water is alwa3^s of the greatest importance in defining the species and in readily 

 recognizing them, for the nmnber of definite and readily recognized constant 

 characters in amoebas is very small. The probability is strong that any 

 species of amoeba may be characterized by a definite degree of resistance of its 

 surface-layer expressed quantitatively in terms of concentration of sea- water. 



This preHminary survey of the marine amoebas indicates that the sea is at 

 least quite as rich in these organisms as fresh water. 



Birds observed on the Florida Keys and the Southern End of the Mainland of 

 Florida in 1919, by Paul Bartsch. 



Dec. 28-31. — Along the coast of Florida only a few immature laughing gulls and 

 man-o'-war birds were seen. 



Jan. 1. — Entering the harbor of Key West in the afternoon, we saw a man-o'-war 

 bird chasing a royal tern. 



Jan. 2. — In a trip to the United States Bureau of Fisheries station, 1 saw only a num- 

 ber of little sparrow hawks, 8 yellow palm warblers, 2 mocking-birds, 6 man-o'-war birds, 

 many laughing gulls, mostly immature, a few royal terns, 2 belted kingfishers, 2 Florida 

 ground doves, 2 Ward's herons, 1 great white heron, 4 brown pelicans, and a number of 

 turkey vultures. 



Jan. 3. — Sailing for the Tortugas, a "southwester" forced us to seek shelter behind 

 the Marquesas. Only a couple of man-o'-war birds and a few brown pelicans were seen. 



Jan. 4. — In the same position, only a few brown pelicans and a couple of man-o'-war 

 birds were listed. 



Jan 5. — While carefully examining the sand beaches, etc., in order not to miss any 

 birds that prefer particular habitat, we saw only a catbird and 4 ospreys, one pair having 

 a nest containing two eggs in advanced incubation, 1 great white heron, 3 Ward's herons, 15 

 brown pelicans, 5 belted kingfishers, 11 yellow palm warblers, 4 Florida ground doves, 



