CILIATES 



173 



membranes, the outer one being continuous and providing the 

 limiting membranes of the cilia, and the middle and inner layers 

 joining to form the discontinuous but closely fitted alveoli 

 (Figs. 70 and 71, PL XIX). 



Text-figure 12. Schematic drawings of sections through a 

 cilium and surrounding structures in Colpidium. Top: transverse 

 section showing continuous outer membrane and alveoli of 

 silverline system. Mucigenic body in secondary meridian at left; 

 secondary meridian at right enlarged above. To right of kineto- 

 some are three sections of kinetodesmal fibrils and row of fibrils 

 composing longitudinal band. To left of cilium are oblique sections 

 of two fibrils of transverse band. Lower left: longitudinal section 

 in an idealized plane just barely to right of primary meridian. 

 Postciliary fibrils posterior to kinetosome; kinetodesmal fibril 

 anterior to kinetosome. Lower right: cross-sections through 

 cilium base at successively deeper levels as indicated by lines, a, b, 

 and c on other diagrams. Transverse fibrils to left of (below) cilia 

 in sections a and b. Parasomal sac and fused pellicular ring in 

 section b. Kinetodesmal and postciliary fibril attachments to 

 kinetosome shown in section c. From Pitelka, 1961a. 



This new picture represents a considerable departure from 

 some, at least, of the classical views of the silverline system inas- 

 much as it is seen to be an arrangement of membranes and not of 



