MORPHOLOGY 47 



Cilia. The cilia are the organella of locomotion and food- 

 capturing found in the Ciliophora. They seem to serve often as 

 a tactile organella. The cilia are fine and more or less short proc- 

 esses of ectoplasm and occur in large numbers in the majority 

 of the Holotricha. They may be uniformly long, as in Protocihata, 

 or may be of different lengths, being longer at the extremities, on 

 certain surfaces, in peristome or in circumoral areas. Ordinarily 

 the cilia are arranged in longitudinal, oblique, or spiral rows, 

 being inserted on either the ridges or the furrows. Again the cilia 

 may be confined to certain parts or zones of the body. 



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 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). 



The cilia are often present in a certain area more densely than 

 in other parts of body and, consequently, such an area stands out 

 conspicuously, and is sometimes referred to as a cihary field. If 

 this area is in the form of a zone, it may be called a ciliary zone. 

 Some authors use pectinellae for short longitudinal rows or trans- 

 verse bands of close-set cilia. In a number of forms, such as Coleps 

 Stentor, etc., there occur, mingled among the vibratile cilia, 

 immobile stiff cilia which are apparently solely tactile in function. 



In the Hypotricha, the ciHa are largely replaced by cirri, al- 

 though in some species both may occur. A cirrus is composed of 

 a number of cilia arranged in 2 to 3 rows which fused into one 

 structure completely (Figs. 11, 12), which was demonstrated by 

 Taylor. Klein also showed by desiccation that each marginal 

 cirrus of Stylonychia was composed of 7 to 8 ciha. In some in- 

 stances, the distal portion of a cirrus may show two or more 

 branches. The cirri are confined to the ventral surface in Hypo- 

 tricha, and called frontal, ventral, anal, caudal, and marginal 

 cirri, according to their location (Fig. 11). Unhke the cilia, the 

 cirri may beat in any direction so that the organisms bearing 

 them, show various ways of locomotion. Oxytricha, Stylonychia, 



