General Morphology of the Protozoa 19 



a thin argentophilic layer covering the axial filament and tapering distally 

 to a granular "end-organ" (132), Electron micrographs indicate that the 

 unfixed, dehydrated axoneme is composed of fibrils in Paramecium, 

 whereas a sheath is suggested merely by possible remnants of an envelop- 

 ing layer (102, 199). 



In certain ciliates an accessory "ciliary corpuscle" (30) is attached to 

 the basal granvde; in some instances, the accessory body may be mito- 

 chondrial in nature (26). Two accessory granules have been reported in 

 certain ciliates (132). A slender fibril, the ciliary rootlet, extends inward 

 from the basal gianule in some ciliates, but is said to be absent in certain 

 primitive species (29). From many of the basal granules in Opalijia 

 obtrigonoidea (Fig. 1. 11, G), fibrils extend dorso-ventrally through the 

 cytoplasm to end in basal granules on the opposite side of the body (34). 

 Whether these fibrils are homologous with the ciliary rootlets of other 

 ciliates is uncertain. 



Cilia lie in meridional or spiral rows in the less specialized ciliates. 

 Although such a pattern is usually rather constant within a species, 

 changes from spiral to meridional to spiral, and even a reversal of the 

 spirals, occur in certain species with complex life-cycles (150). Individual 

 cilia, in ciliates with sculptured pellicles, may emerge from grooves, from 

 the margins of such grooves, or from individual pits in different cases. 



The simple cilium is the primitive locomotor structure in ciliates. 

 Many species possess compound organelles which have arisen by fusion of 

 cilia in longitudinal or transverse rows, or in tufts. Such organelles are 

 known as undulating membraries, memhranelles and cirri. An undulating 

 membrane, formed by the fusion of one or more longitudinal rows of 

 cilia, lies in the peristome (oral "groove") of various species. Rippling 

 movements of the membrane drive particles to the cytostome. This organ- 

 elle may not be permanent in quite the same sense that cilia are so 

 considered, since the membrane of Blepharisma undulans may break up, 

 spontaneously or after injury, into individual cilia. The cilia eventually 

 fcuse again into an undulating membrane (24). Memhranelles, which are 

 more or less triangular flaps formed by fusion of two or more transverse 

 rows of cilia, are found especially in the peiistomial area (Fig. 1. 15, H). 

 Each membranelle of Spirostomum ambiguum contains a double row of 

 cilia whose basal granules end in a plate parallel to the surface of the 

 body (Fig, 1, 11, E), A basal lamella, extending inward from the plate, 

 tapers to an end-thread which joins a basal fibril in the endoplasm (8), 

 Cirri, characteristic of the Hypotrichina, consist of tufts of cilia probably 

 embedded in a matrix (Fig. 1, 11, C, D). The number of cilia varies with 

 the size of the cirrus — in Oxytricha fallax, for example, three or more in 

 the small marginal cirri and 8-18 in the ventral, frontal, and anal cirri 

 (146). 



