General Morphology of the Protozoa 23 



and also in Podophrya (Suctorea), this primitive system obviously is not 

 limited to unspecialized ciliates. 



Specialization of the silver-line system involves first an increase in 

 diameter of the mesh, so that a single mesh comes to enclose a group of 

 ectoplasmic alveoli. As the mesh widens, the silver-lines decrease in num- 

 ber and begin to parallel the rows of basal granules (Fig. 1. 12, A). In 

 meridional ciliation, the system may be reduced to ineridians bearing the 

 basal granules and sometimes joined by transverse commissures (Fig. 1. 

 12, C) — so-called striation-systems. Each meridian is sometimes double 

 (Fig. 1. 12, D). Or the silver-line may be a bundle of fibrils. In Colpidiitm 

 colpoda (132), each meridian is said to split just behind the cytostome 

 into primary and secondary meridians. The basal granules lie very close 

 together in the fused anterior meridians. Posteriorly, the basal granules 

 in the primary meridians are spaced at fairly short and rather regular 

 intervals; those in the secondary meridians, at longer and more irregular 

 intervals. 



In addition to the basal granules of cilia, the silver-line system includes 

 trichocyst-granules and protrichocyst-granules, all three types being con- 

 sidered '"relator-granules" which relate the corresponding structures to 

 the silver-lines. The protrichocyst-granules also have been considered 

 tec tin-granules (12), which presumably are extruded through secretory 

 pores in the pellicle (65). The relator-granules, especially the basal gran- 

 ules, may persist after their organelles have disappeared in phylogeny, 

 and thus represent persistent traces of much more primitive conditions 

 (132). 



Both the fibrils and the relator-granules are said to lie at the same 

 level in the ectoplasm (132). However, the network ("indirect system" 

 of Klein) apparently does not occupy the same plane as the basal gran- 

 ules and longitudinal fibrils in Paramecium caudatum, since the latter are 

 not in focus in photomicrographs which show the network clearly (67). 

 Lund (145) concluded that the peripheral "network" in P. multimicro- 

 nucleatum represents pellicular ridges upon which silver is deposited in 

 dried specimens. The correlation between pellicular markings and the 

 silver-line pattern also has been stressed by Jacobson (100). Therefore, 

 the exact nature of Klein's superficial network remains uncertain. The 

 silver-line meridians, which join the basal granules, appear to be sub- 

 pellicular. 



Neuroneme system 



This system (64, 67), demonstrable by the techniques of Gelei 

 and Horvath (68), joins the basal granules and possibly corresponds to 

 the meridians of Klein. In sectioned material, the neuronemes of Para- 

 mecium caudatum (Fig. 1. 13, C) appear as zigzag lines joining the basal 

 granules to the more superficial trichocyst-granules (64). The neuronemes 

 are not continuous with the superficial silver-line network of Klein. 



