SCANNING ELECTRON MICROSCOPIC EXAMINATION OF CA2 + -INDUCED FOOD VACUOLE FORMATION IN THE CARNIVOROUS MACROSTOMAL FORM OF TETRAHYMENA VORAX, STRAIN V2S.

The addition of Ca**2** plus to the potentially carnivorous macrostomal cell type of the polymorphic ciliate, Tetrahymena vorax, V//2, induces each cell in the population to seal-off its prey receptacle, the cytopharyngeal pouch, to form a large empty food vacoule. When this process is viewed by SEM, closure begins by a decrease in the size of the cytostomal opening as the right ribbed wall and part of the ribbed posterior ventral wall project into this opening. A structure, believed to be the fine filamentous reticulum, which underlies the left margin of the ribbed wall, is described. These results are discussed in terms of prey capture and in terms of the fine filamentous reticulum. The latter may be a Ca**2** plus -dependent force-generating system which participates in closure of the cytostomal opening.