Cilic 



643 



garded as composite bodies comprising numerous cilia arising from a num- 

 ber of basal granules in a circular or ovoid field/"'"' The ciliary elements ad- 

 here closely to one another in a viscous matrix. The cilia of such a cirrus 

 beat in unison. Membranelles of the adoral region of manv pcritrichs are 

 small platelets of fused cilia beating synchronously. The undulating mem- 

 branes of ciliates such as Blepharisma are long rows of cilia, each adhering 

 to its neighbors. The compound character of the membrane mav often be 

 demonstrated by its fragmentation by appropriate manipulation with a 

 microdissecting needle.'^ The component cilia, when separated from one an- 

 other, beat quite independently; when they have reunited, the characteristic 

 coordinated activity giving rise to the undulatory movement is restored. 

 Such an activity is the result of the metachronic wave of ciliary activity pro 

 cceding at right angles to the effective and recoverv strokes. 



Fig. 242. Electron micrograph of a cilium from Paramecium, shadow-cast with chromium. 



From Jakus and Hall.™ 



Characteristics of Ciliary Movement. The activity of any cilium may be 

 resolved into one or another, or some combination, of three fundamentally 

 different types of movement.-*' One of these is pendular movement in 

 which the cilium bends back and forth, flexing only at its base. No differ- 

 ence in the form of the cilium is observed between the effective and the 

 recovery phases of its stroke, the former simply occurring more rapidly than 

 the latter. 1 his type of movement is seen in the cirri of hypotrichs. A second 

 type of movement is a flexural one. Bending begins first at the tip of the 

 cilium and passes toward its base; in recovery, the cilium progressively 

 straightens from base to tip. Such hooklike bending is observed in the 

 latero-frontal cilia of lamellibranch gills. The third fundamental type of 

 ciliary activity is undulatory movement. This type is characteristic of flagella. 

 In this type of movement waves pass along the flagellum from base to tip of 

 the organelle, apparenth' ne\er in the rexerse direction. 



A type ol ciliary activity involving a combination of pendular and flexural 

 activities is obserxed in the frontal cilia of the gill of Mytihis'-*' (Fig. 243^. 

 The effective stroke is a rapid, stiffly sweeping, pendular movement with the 



