50 



PROTOZOOLOGY 



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

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

 conspicuously, and is sometimes referred to as a ciliary 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 transverse 

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

 tor, etc., there occur, mingled among the vibratile cilia, immobile 

 stiff cilia which are apparently solely tactile in function. 



cpg 



Fig. 12. Diagrams of cirrus and membranella of Euplotes eurystomus, 

 X1450 (Taylor), a, an anal cirrus in side view; b, a membranella; bg, 

 basal granule; cpg, coagulated protoplasmic granules; cr, ciliary root; 

 fp, fiber plate. 



In the Hypotricha, the cilia are largely replaced by cirri, although 

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

 cilia arranged in 2 to 3 rows that fused into one structure com- 

 pletely (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 cilia. In some instances, the distal portion of a 

 cirrus may show two or more branches. The cirri are confined to the 

 ventral surface in Hypotricha, and called frontal, ventral, anal, 

 caudal, and marginal cirri, according to their location (Fig. 11). Un- 

 like the cilia, the cirri may move in any direction so that the organ- 

 isms bearing them, show various types of locomotion. Oxytricha, 



