PROTOZOA AS CELLS 35 



Roth (1960a), studying ultrastructure of normal, untreated 

 amebae, observed vacuoles well within the cytoplasm with mem- 

 branes bearing the fine plasmalemma fringe. Other vesicles lacked 

 the fringe; some had dense granules on their membranes; some 

 vesicle membranes were darkened by staining with phospho- 

 tungstic acid, while others were not. Roth tentatively suggested 

 a sequence of changes in membrane properties, including permea- 

 bility. Demonstration of such a sequence will require the use of 

 labels that are capable of entering the cytoplasm of the ameba. 



Chapman-Andreson and Nilsson (1960) were unable to see any 

 difference in the appearance of pinocytotic and other intracellular 

 membranes and the plasmalemma, but their micrographs were 

 not sufficiently detailed to reveal membrane structure. They 

 noted the presence of small vesicles in the region of pinocytosis 

 channels, similar to those surrounding the contractile vacuole, 

 and speculated that these might be associated with water removal 

 from the channels. 



Wohlfarth-Bottermann (1960b), in an electron-microscope 

 study of the small free-living ameba, Hyalodisc/is, observed 

 abundant vesicles, especially at the posterior end of the cell, that 

 still bore the hairy plasmalemma fringe and thus could be 

 identified as pinocytosis channels or vacuoles. Other vesicles 

 within the endoplasm had no fringe but a distinct three-ply 

 structure (Fig. 13, PL IV). Still others, apparently sectioned at 

 similar angles and often continuous with three-ply membranes, 

 appeared to be limited by simple single-ply membranes. Further- 

 more, some of the three-ply membranes were fragmented, 

 suggesting release of vesicle contents into the cytoplasm. Usually, 

 fragmented membranes are attributable to polymerization damage 

 in the plastic blocks, but Wohlfarth-Bottermann's specimens 

 were embedded in Vestopal, which presumably reduces poly- 

 merization damage to a minimum, and the general appearance of 

 his sections indicated superior fixation for ameba protoplasm, as 

 well as high-resolution micrography. Taken at face value, his 

 results not only suggest a sort of membrane fragmentation not 

 certainly seen elsewhere, but also cast some doubt on the unit- 

 membrane concept. The use of labeled proteins as pinocytosis 

 inducers with Hyalodiscus might yield highly significant information. 



Amebae again provide the bulk of current information on the 



