Fine Structure of the Silverline and Fibrillar Systems of Three Tetrahymenid Ciliates*

Abstract

Application of fragmentation and thin‐sectioning techniques to Tetrakymena pyriformis, Colpidium compiles and Glaucoma chattoni has permitted an analysis of the ultra‐structure of their silverline and fibrillar systems. The classical silverline system consists of a mosaic of flat, membrane‐bound blisters whose rims represent the sites of selective silver deposition. Cilia and protrichocysts emerge between adjacent blisters. I The pellicle consists of the membranes outlining the blisters, overlain by a continuous outer membrane that covers the whole cell and cilia. Fibrillar structures, which are not argentophilic, include: (1) tapering, striated kinetodesmal fibers arising singly from the kinetosomes, passing to the right and anteriad, and overlapping to form a loose bundle accompanying each kinety; (2) a longitudinal fibril band immediately beneath the pellicle at the right of each kinety, consisting of overlapping individual fibrils; (3) a transverse band of fibrils arising at the left side of each kinetosome and passing to the left under the pellicle; and (4) a set of postciliary fibrils arising at the right posterior edge of each kinetosome and passing posteriad under the pellicle. The fibrils of sets (2), (3), and (4) all are about 20 Mμ in diameter and appear tubular in cross‐section; they are very unlike the heavier, solid kinetodesmal fibers. None of the fibril sets directly interconnect, although transverse and postciliary fibrils end in the vicinity of the longitudinal fibril band.

ULTRASTRUCTURE OF MUCOCYSTS AND PELLICLE OF TETRAHYMENA PYRIFORMIS

“…2 and 3) may be profiles of mucocysts. Similar electron microscopically empty structures have been referred to as protrichocysts (13) or mucigenic bodies (12), and are considered here to be mucocysts prior to discharge. After discharge, the material is difficult to discern as it has almost the same density as the background.…”

“…The outer pellicular membrane (opm) appears to be thicker than the inner pellicular membrane As described by Pitelka (12,13), the inner pellicular membrane may be continuous with the cytoplasmic membrane at sites at which mucocysts are in contact with the outer pellicular membrane (Figs. 13 to 15).…”

“…The outer parts of the mucocysts in Colpidium campylum were found to be bounded by a membrane which is not continuous with any cytoplasmic or pellicular membrane (13).…”

“…It appears to be of a mucoid or gelatinous nature and may contribute to the formation of protective coatings (12). Mucocysts are aligned in rows along the primary and secondary meridians in Tetrahymena pyriformis and Colpidium campylum (13) and more or less randomly distributed over the cell surface in Colpidium colpoda (1).…”

“…The discharged material consists of structurally highly organized filaments (trichocysts) or amorphous mucoid substances. The structures containing the amorphous material are variously referred to as protrichocysts (13), mucoid trichocysts (13), mucigenic bodies (12), or secretory ampules (1, 2). The latter four terms have apparently been used to describe similar or identical structures which we will refer to as "mucocysts."…”