CILIATES 183 



Elsewhere rather large (up to 7 ft in diameter) masses of con- 

 voluted, smooth-surfaced double lamellae are infrequently seen; 

 lipid droplets often are present nearby. The significance of these 

 membranous structures is unknown. Nuclear morphology has 

 been described in Chapter 2. 



Kappa, the DNA-containing cytoplasmic particle responsible 

 for the killer trait in Paramecium aurelia, shows, according to 

 Dippell (1958), similarities to bacteria or rickettsiae. Each kappa 

 particle is surrounded by a double membrane and filled with a 

 diffusely filamentous material enclosing small, dense, irregular 

 granules. Some kappa particles contain an inclusion consisting of 

 concentric cylindrical membranes surrounding a granular core. 

 Beale and Jurand (1960) conclude similarly that the mu particles 

 of another killer strain of P. aurelia are bacteria modified somewhat 

 by a long history of obligate symbiosis. 



In summary, most of the structures seen by light microscopists 

 have now been identified in electron micrographs of Paramecium 

 and the tetrahymenids. The pellicle comprises three membranes — 

 the outer continuous one and the middle and inner ones outlining 

 the alveoli of the silverline system. Three morphologically dis- 

 tinguishable kinds of fibrils are seen: (1) the solid, striated 

 kinetodesmal fibrils ; (2) the very orderly tubular, 20-m/z fibrils of 

 the tetrahymenids ; and (3) the filaments of the infraciliary lattice 

 of Paramecium and of the buccal zone in both. Paramecium and the 

 tetrahymenids. According to Roth, the last two categories would 

 be the same, but micrographs showing a tubular nature for the 

 filaments in cross-section are not available, and their random 

 packing and tendency to appear sinuous give them a decidedly 

 different appearance from the very precisely arranged tubular 

 fibrils of group 2. Conversely, it hardly needs emphasizing that 

 fibrillar structures that look alike in electron micrographs are not 

 necessarily alike in any other property. 



Order Gymnostomatida 



Embarking on a systematic tour of the ciliates we meet first a 

 group of great significance, the Order Gymnostomatida. Accord- 

 ing to Corliss (1956, page 81), "The most primitive forms [of 

 gymnostomes], with their apically located cytostome, simple axis 

 of symmetry, and uniform somatic ciliature, may well be con- 



