48 PROTOZOOLOGY 



They may be uniformly long, as in Protociliata, or may be of differ- 

 ent lengths, being Ipnger at the extremities, on certain areas, in 

 peristome or in circumoral areas. Ordinarily the cilia are arranged in 

 longitudinal, oblique, or spiral rows, being inserted either on the 

 ridges or in the furrows. Again the cilia may be confined to certain 

 parts or zones of the body. 



Fig. 10. Diagrams of cilia (Klein), a, Coleps; b, Cyclidium glaucoma; 

 c, Colpidi'uni colpoda. af, axial filament; bg, basal granule; cf, circular 

 fibril; cs, cross-striation; sg, secondary granule. 



Each cilium originates in a basal granule situated in the deeper 

 part of the ectoplasm and, in a few species, a cilium is found to be 

 made up of an elastic axial filament arising from the basal granule, 

 and the contractile sheath. Gelei observed in flagella and cilia, lipoid 

 substance in granular or rod-like forms which differed even among 

 different individuals of the same species; and Klein found in many 

 cilia of Colpidium colpoda, an argentophilous substance in granular 

 form much resembling the lipoid structure of Gelei and called them 

 "cross-striation" of the contractile component (Fig. 10). 



