OBSERVATIONS ON FEEDING OF AMEBA 35 



been maintained by Rhumbler ('05 and '10), McClendon ('12) 

 and others. 



Feeding on rotifers. Rotifers belonging to the genus Rotifer 

 were frequently seen in our cultures, sometimes in abundance. 

 In one of the cultures, for more than two weeks, the amebae were 

 found to feed almost exclusively on these animals. Fully half 

 of the specimens examined were either attached to rotifers or 

 contained different parts of them in their food-vacuoles (fig. 1). 

 It seems extraordinary that an ameba should be able to capture 

 and ingest animals relatively so powerful and active as are these 

 rotifers. 



The whole process of feeding w^as not followed through in any 

 given individual, but practically all stages in it were repeatedly 

 observed in different ones. The following account is based upon 

 these observations. 



The rotifers in the cultures frequently became attached by 

 means of an adhesive secretion at the posterior end and remained 

 for considerable periods of time. While thus attached the ame- 

 bae in wandering aimlessly about came in contact with them 

 from time to time. When this occurred they usually surrounded 

 the foot, and to this and the substratum they adhered so firmty 

 that the rotifers could not escape. Soon after an ameba has 

 thus surrounded the foot of a rotifer it begins to flow up around 

 its body. This appears to cause the rotifer to contract sharply 

 forcing the ameba back. After a time the rotifer again stretches 

 out and then the ameba again starts to flow up around it, after 

 which the rotifer again contracts and forces the ameba back. 

 Thus they continue to struggle, sometimes for days (fig. 2). In 

 the meantime the foot of the rotifer begins to digest or liquefy, 

 and this process gradually extends out farther and farther until 

 the animal is killed or until the injury is so great that the contrac- 

 tions and extensions are not strong enough to prevent the ameba 

 from surrounding it. In several cases the rotifers were seen to 

 move considerably after they had been swallowed. This is espe- 

 cially true of young individuals attached to the mother and swal- 

 lowed with her. In a few cases such individuals were apparently 

 uninjured, for they were seen to swim away after having been 

 released by destroying the amebae (fig. 2). 



