OBSERVATIONS ON AMEBA FEEDING ON ROTIFERS, 

 NEMATODES AND CILIATES, AND THEIR BEAR- 

 ING ON THE SURFACE-TENSION THEORY 



S. O. MAST AND F. M. ROOT 



From the Zoological Laboratory of the Johns Hopkins University 



FIVE FIGURES 



For several years past we have occasionally collected amebae 

 in a brick-yard pond in the vicinity of Baltimore. These am- 

 ebae are large lobose forms which correspond, at least super- 

 ficially, with the ordinary descriptions of Ameba proteus (fig. 1). 

 They feed almost exclusively on living organisms and thri\'e re- 

 markably well in hay-infusions. When the infusoria in such cul- 

 tures begin to decline the amebae begin to increase rapidly and 

 frequently become so numerous that the substratum on which 

 they are found appears distinctly grayish; but as the infusoria 

 diminish the amebae decrease in numbers and eventually appar- 

 ently disappear entirely, but they usually appear again if more 

 hay and water is added so as to induce the infusoria to develop. 

 We have found this to occur in cultures which had been inactive 

 as long as four months. By occasionally adding a little hay and 

 water, we have succeeded in keeping, in ordinary glass dishes, 

 cultures of these amebae for several years. They could, no 

 doubt, be kept indefinitely. 



In connection with other work on these amebae we have inci- 

 dentally observed some remarkable phenomena associated with 

 feeding. Some of these phenomena were of such a nature that 

 it is impossible to account for them on the assumption that 

 movement in ameba is exclusively due to changes in surface 

 tension as is maintained by Biitschli ('92), Ryder ('94), Jensen 

 ('05), Verworn ('09) and others, and they seem to indicate that 

 the role played by surface tension is far less significant than has 



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THE JOURNAL Or EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 1 



