OBSERVATIONS ON FEEDING OF AMEBA 47 



indicate, as Hofer ('90) concludes, that the nucleus acts as a 

 regulatory center. This conclusion is also supported by the 

 work of Mr. H. S. Willis carried on in our laboratory and now 

 in press in the Biological Bulletin. Gruber ('12) and others, 

 however, oppose this construction, although they obtained 

 results similar to those obtained by Hofer and Willis. 



The conclusion reached above regarding surface tension is in 

 harmony with that reached by Jennings ('04) in his observations 

 on the rolling movement in ameba and by Bellinger ('06) in his 

 observations on the walking movement. It is also supported 

 by Kepner and Taliaferro '(13) in their interesting observations 

 on the process of feeding. 



SUMMARY 



1 . Certain amebae at times feed almost exclusively on rotifers, 

 at others they feed largely on paramecia. 



2. They capture the rotifers by flowing around the foot at the 

 point of attachment to the substratum. After they have sur- 

 rounded the foot they begin to flow out over the body. The roti- 

 fer responds by contracting and forcing the ameba back, after 

 which it extends again and the ameba again begins to flow out 

 over it, etc. In the meantime the foot begins to digest and grad- 

 ually the rotifer weakens. ^ Thus they continue sometimes for 

 days before the rotifer is swallowed. 



3. When amebae are feeding on paramecia they assume a sort 

 of mushroom shape with a serrate edge consisting of numerous 

 short pseudopods. The paramecia tend to come to rest between 

 and under these pseudopods by which they are usually sur- 

 rounded, but sometimes the ends of the pseudopods approach 

 each other before they are fully extended and cut the Parame- 

 cium in two. 



4. To cut a Paramecium in two with a fine glass fiber it re- 

 quires a pressure of approximately 9 mgm. If the pseudopods 

 have the same cutting quality as the glass fiber and if their move- 

 ment is due to a change of surface tension, it requires to perform 

 the work involved, a reduction in surface tension of at least 1118 

 dynes per centimeter at the tips of the pseudopods. 



