38 



S. O. MAST AND F. M. ROOT 



When the amebae are feedmg on infusoria they assume some- 

 what the form of a mushroom, consisting of a flat disk-like por- 

 tion with a serrate edge composed of numerous short pseudopods, 

 supported by a basal portion (fig. 4). When superficially ob- 

 served the animals, in this form, appear to be perfectly quiet. 



0.3 min 



Fig. 3 Camera sketches of an ameba feeding on a nematode: mm, projected 

 scale. 



A Ameba and nematode as they appeared shortly after they were discovered, 

 December 3, 10.20 a.m. At this time the protruding anterior end of the worm 

 was violently bending back and forth. Fifteen minutes later it was entirely 

 surrounded by the ameba. 



B The same specimen, 1 p.m., showing the worm coiled up. 



The pseudopods are, however, continuously in a state of flux, 

 alternately contracting and expanding slightly. 



In a given culture containing a considerable number of amebae 

 in this form and numerous infusoria I often saw some of the in- 

 fusoria come to rest and remain quiet for some time in the angle 

 formed between the substratum and the projecting edge of the 

 disk-like portion of the amebae. When this occurred a stout 

 pseudopod usually appeared on either side of the infusorian, also 



