CILIATES 193 



Trujillo-Cenoz (1959). The non-contractile stalk in Campanella, 

 Opercularia, and Epistylis consists of a cylindrical bundle of 

 uniquely modified cilia, surrounded by a homogeneous sheathing 

 membrane apparently elaborated by an ectoplasmic lip around the 

 scopula. Sections through the scopula of Campanella parallel to 

 its surface show concentric rings of typical basal bodies. Conven- 

 tional cilia, complete with 11 fibrils and membrane, arise from 

 the kinetosomes and are clearly recognizable as such in sections 

 cut near the cell end of the stalk. Their diameter increases rapidly, 

 so that their membranes come into contact with one another and 

 shortly their axial fibrils disappear. What remains then is a bundle 

 of ciliary membranes forming tubules about 350 to 400 m/x in 

 diameter. Longitudinal sections demonstrate that the membranes 

 have become fibrous; a diagonal lattice of criss-crossed fine 

 filaments (5 to 10 m/x in diameter) is evident. However, apparent 

 continuity of filaments through adjacent tube walls suggests that 

 a matrix material may contribute to this structure. 



In Opercularia the situation is similar, but here it appears that 

 the peripheral fibrils, rather than the membrane, persist in the 

 stalk, embedded in a low-density matrix. The fibrils in this case 

 acquire a distinct transverse striation, with a period of about 22 m/x 

 near their origin and up to 44 m/x distally. In Epistylis the stalk is 

 again composed of packed tubules; here they appear as thin- 

 walled cylinders except near the base (the earliest part formed) of 

 the stalk where nine fibrils are apparent in their walls. 



The contractile stalks of the vorticellids contain an elastic 

 substance that may surround and enclose the myoneme or may 

 simply parallel it. The elastic element oiZoothamnium is composed 

 of striated cylinders that are ciliary in origin, embedded in a 

 homogeneous matrix (Fig. 78, PL XXI). Carchesium stalks like- 

 wise contain banded fibers that are ciliary outgrowths. In 

 Vorticella the fibrils are few in number, unhanded, and attached 

 throughout their length to the sheathing membrane of the stalk. 



The contractile myoneme in these species, when examined at 

 high resolution, is seen to consist of a bundle of very fine filaments 

 2 to 4 m/x in width and of indefinite length. In cross-section the 

 bundle appears alveolar, enclosing many circular spaces identified 

 by Sotelo and Trujillo-Cenoz as a system of membranous canaliculi. 



This stalk myoneme in vorticellids is directly continuous with 



