26 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



mechanisms, and a considerable amount of information already 

 available on its fine structure provides an added attraction. 



In amebae, contractile vacuoles move about through the 

 protoplasm and presumably have no morphologically determined 

 discharge pore. Light microscopy indicates a rather thick vacuolar 

 membrane and surrounding this a layer of gelated protoplasm and 

 a cloud of so-called beta-granules. In the electron microscope the 

 vacuole in Amoeba pro tern, Pelomyxa carolinensis, and Hartmannella 

 rbysodes (Greider, Kostir, and Frajola, 1958; Pappas, 1959; Mercer, 

 1959) is limited by a typical unit membrane. The protoplasm 

 surrounding it is filled with tubules and vesicles, 20 to 200 m/x in 

 diameter. This vesicular zone varies from 0-5 to 2 [i in thickness, 

 probably depending on the stage in the vacuolar cycle. Beyond 

 it is a halo of mitochondria (the beta-granules of the light micro- 

 scopist), irregularly crowded while the growing vacuole is small 

 but becoming aligned in a compact ring as the vacuole enlarges. 

 Rather frequently, individual vesicles appear to open into the 

 vacuole, and Mercer and Pappas agree in their interpretation of 

 this picture as one suggesting segregation of fluid into membrane- 

 bounded vesicles and tubules, and the emptying of this fluid into 

 the main vacuole by coalescence. The mitochondria presumably 

 provide energy for the segregation, and may in addition be 

 involved in the water transport itself. Vacuoles at the moment 

 of systole in amebae have not been shown. 



A canalicular- vesicular zone surrounding the vacuole has been 

 found in several ciliates, including the suctorian Tokophrya 

 (Rudzinska, 1958), the peritrichs Campanella and Ophrydium 

 (Faure-Fremiet and Rouiller, 1959), and several astomes 

 (de Puytorac, 1960, 1961a). In Tokophrya the vesicles do not 

 appear to be particularly numerous; in the peritrichs and the 

 astomes, on the other hand, the thick cortical zone is permeated 

 by distinctly tubular elements that branch and anastomose and 

 occasionally dilate to form larger vesicles. In all cases, occasional 

 images suggest the opening of tubules or vesicles into the main 

 vacuole. Around the periphery of the spongy zone, membranes 

 of the tubules occasionally appear to be continuous with mem- 

 branes of the endoplasmic reticulum. Mitochondria are variably 

 abundant in the surrounding cytoplasm. 



Relatively long discharge canals lead from the vacuole to the 



