38 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



in a digestive phase; again, his micrographs suggested that the 

 vesicles were forming by a budding process from the vacuole 

 membrane. In addition, Jurand observed minute invaginations of 

 the plasma membrane at the base of the oral cavity, near the site 

 of food vacuole formation. Moller and Rohlich (1961) examined 

 food vacuoles in Tetrahjmena corlissi and again found evidence 

 of pinocvtosis from the main vacuole during digestive phases. 

 Ingested cells were unrecognizable from the first, suggesting 

 some extracellular predigestion in the buccal cavity. 



Flagellar Apparatus 



Cilia and flagella were among the first objects of electron- 

 microscope study by biologists, for the obvious reason that, until 

 thin-sectioning techniques were developed, they were almost the 

 only protoplasmic structures in organisms above the bacteria that 

 could be examined without resorting to cell fragmentation. A 

 number of early investigators turned their attention to animal 

 sperm tails (see reviews by Fawcett, 1958, 1961) and to the flagella 

 of protozoa and metazoa (Schmitt, Hall, and Jakus, 1943; Brown, 

 1945; Jakus and Hall, 1946; Dinichert, Guyenot, and Zalokar, 

 1947; Foster, Baylor, Meinkoth, and Clark, 1947; Pitelka, 1949). 

 The consensus of all these studies, now mainly of historical 

 interest, was that the axis of these vibratile organelles consisted 

 of a number, usually described as nine to 12, of continuous 

 longitudinal fibers, and that these were bound together by a 

 sheath of variable composition and dimensions. In addition, 

 Brown (1945) and Pitelka (1949) demonstrated the presence in 

 several flagellate species of orderly arrays of lateral filaments. 

 None of these observations was totally new, since light micro- 

 scopists (see papers by Brown and Pitelka for references) had 

 detected fibrous axial and filamentous lateral structures. 



In the early 1950's the English botanist Manton and her 

 colleagues, using an ingenious combination of techniques for the 

 electron-microscope study of whole and fragmented small plant 

 flagellates, came to the startling conclusion that the axis in all 

 cases contained precisely 11 longitudinal fibers, and that these 

 were always arranged as a cylinder of 9 fibers about a central pair. 

 The latter, finer than the others and more likely to disintegrate 



