CILIATES 171 



conjugating pairs of T. piriformis, Pitelka (1961a) has analyzed in 

 detail the cortical structures characteristic of the group, and Roth 

 and Minick (1961) have observed some morphological features 

 of dividing cells of Tetrahymena. 



The silverline system typical of all three genera is illustrated in 

 Fig. 69, PL XIX. The primary meridians, except those behind the 

 mouth, extend from pole to pole and bear the kinetosomes and 

 smaller argentophilic granules which are "protrichocysts" or 

 mucigenic bodies. Secondary meridians bearing mucigenic bodies 

 but no kinetosomes typically alternate with the primaries but may 

 be interrupted or absent; they merge with the primaries anteriorly 

 and posteriorly. Electron-micrographs of pellicle fragments show 

 the meridians as slender, sinuous lines with occasional expansions, 

 often circular in outline, that represent the points of attachment 

 of mucigenic bodies. 



Examination of sections reveals that the entire surface of the 

 cell is covered by a continuous unit membrane (Text-fig. 12). 

 Immediately beneath this is a mosaic of flat, membrane-bounded 

 alveoli* whose contiguous rims are the sites of silver deposition 

 and thus define the silverline system. Each alveolus is elongate, 

 occupying the area between a primary and the adjacent secondary 

 meridian; transverse interruptions occur at apparently random 

 intervals. Cilia and mucigenic bodies emerge from the underlying 

 ectoplasm between adjacent alveoli. Ordinarily the alveoli are so 

 flat that the space within them is almost non-existent, but under 

 some conditions — presumably of suboptimal fixation — they 

 become inflated and their outlines are clearly identifiable. Thus 

 over most of the body surface the pellicle consists of three parallel 



* In a previous description of this system (Pitelka, 1961a), the pellicular 

 spaces were called blisters. Several of my colleagues have protested that this 

 term carries pathologic connotations "and hence is unsuitable for normal 

 structures. De Puytorac (1961b), describing the equivalent system in an 

 astome ciliate, uses the term vesicles, but it is employed so widely for miscel- 

 laneous intracytoplasmic spaces that confusion seems likely. Peribasal space, 

 introduced by Ehret and Powers (1959) for Paramecium, seems unnecessarily 

 cumbersome and descriptively inaccurate when applied to other ciliates. I 

 am indebted to Dr. B. Parducz for pointing out to me that the structures seen 

 are in all probability identical to those described by Butschli (1887-1889) as 

 superficial alveoli. It is a pleasure to acknowledge the priority as well as the 

 suitability of this term. 



