108 



PROTOZOOLOGY 



Ciliary movement. The cilia are the locomotor organella pres- 

 ent liermanently in the ciliates and vary in size and distribution 

 among different species. Just as flagellates show various types of 

 movements, so do the ciliates. Individual cilium on a progressing 

 ciliate bends throughout its length and strike the water so that 

 the organism tends to move in a direction opposite to that of the 

 effective beat, while the water moves in the direction of the beat 

 (Fig. 45, a-d). In the Protociliata and the majority of holotrich- 

 ous and heterotrichous ciliates, the cilia are arranged in longi- 



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f /"\ 



:a 



9 







Fig. 45. Diagrams illustrating ciliary movements (Verworn). a-d, 

 movement of a marginal cilium of Urostyla grandis (a, preparatory and 

 b, effective stroke, resulting in rapid movement; c, preparatory, and d, 

 effective stroke, bringing about moderate speed); e, metachronous 

 movements of cilia in a longitudinal row. 



tudinal, or oblique rows and it is clearly noticeable that the ciUa 

 are not beating in the same phase, although they are moving at 

 the same rate. A cilium (Fig. 45, e) in a single row is slightly in 

 advance of the cilium behind it and slightly behind the one just 

 in front of it, thus the cilia on the same longitudinal row beat 

 metachronously. On the other hand, the cilia on the same trans- 

 verse row beat synchronously, the condition clearly being recog- 

 nizable on Opalina among others, which is much like the waves 

 passing over a wheat field on a windy day. The organized move- 

 ments of cilia, cirri, membranellae and undulating membranes 

 are probably controlled by the neuromotor system (p. 55) which 



